Base station signaling in a wireless network

ABSTRACT

A first base station may communicate with a second base station regarding a wireless device and handover. The communication may involve indicating carriers associated with the wireless device. The carriers may be of different types, and may have differences regarding reference signals. The first base station may cause a handover of the wireless device from the first base station to the second base station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/864,894,filed Jan. 8, 2018, now U.S. Pat. No. 10,517,084, which is acontinuation of application Ser. No. 14/941,147, filed on Nov. 13, 2015,now U.S. Pat. No. 9,867,178, which is a continuation of Ser. No.14/042,840, filed on Oct. 1, 2013, now U.S. Pat. No. 9,220,104, which isa continuation of application Ser. No. 13/938,306, filed Jul. 10, 2013,now U.S. Pat. No. 8,571,056, which is a continuation of application Ser.No. 13/791,535, filed Mar. 8, 2013, now U.S. Pat. No. 8,526,459, whichis a continuation of application Ser. No. 13/691,720, filed Nov. 30,2012, now U.S. Pat. No. 8,427,976, which claims the benefit of U.S.Provisional Application No. 61/566,670, filed on Dec. 4, 2011, and U.S.Provisional Application No. 61/566,671, filed Dec. 4, 2011, all of whichare hereby incorporated by reference in their entirety.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Examples of several of the various embodiments of the present inventionare described herein with reference to the drawings, in which:

FIG. 1 is a diagram depicting example sets of OFDM subcarriers as per anaspect of an embodiment of the present invention;

FIG. 2 is a diagram depicting an example transmission time and receptiontime for two carriers as per an aspect of an embodiment of the presentinvention;

FIG. 3 is a diagram depicting OFDM radio resources as per an aspect ofan embodiment of the present invention;

FIG. 4 is a block diagram of a base station and a wireless device as peran aspect of an embodiment of the present invention;

FIG. 5 is a diagram depicting example time and frequency resources fortwo downlink carriers as per an aspect of an embodiment of the presentinvention;

FIG. 6 is a diagram illustrating a synchronization channel, data channeland control channel as per an aspect of an embodiment of the presentinvention;

FIG. 7 is a diagram depicting example control and data transmission fordownlink carriers and uplink carriers as per an aspect of an embodimentof the present invention;

FIG. 8 is a diagram depicting example control and data transmission fordownlink carriers and uplink carriers as per an aspect of an embodimentof the present invention;

FIG. 9 is an example flow chart for configuration of non-backwardcompatible carriers as per an aspect of an embodiment of the presentinvention;

FIG. 10 is an example flow chart showing communications between twoneighboring base stations including non-backward compatible carriers asper an aspect of an embodiment of the present invention;

FIG. 11 is an example flow chart for handover between two neighboringbase stations including non-backward compatible carriers as per anaspect of an embodiment of the present invention; and

FIG. 12 is an example flow chart for handover between two neighboringbase stations including non-backward compatible carriers as per anaspect of an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Example embodiments of the present invention implement multicarrier OFDMcommunications. Example embodiments of the technology disclosed hereinmay be employed in the technical field of multicarrier communicationsystems. More particularly, the embodiments of the technology disclosedherein may relate to transmission and reception of control and datatraffic in a multicarrier OFDM communication system.

Example embodiments of the invention may be implemented using variousphysical layer modulation and transmission mechanisms. Exampletransmission mechanisms may include, but are not limited to: CDMA (codedivision multiple access), OFDM (orthogonal frequency divisionmultiplexing), TDMA (time division multiple access), Wavelettechnologies, and/or the like. Hybrid transmission mechanisms such asTDMA/CDMA, and OFDM/CDMA may also be employed. Various modulationschemes may be applied for signal transmission in the physical layer.Examples of modulation schemes include, but are not limited to: phase,amplitude, code, a combination of these, and/or the like. An exampleradio transmission method may implement QAM (quadrature amplitudemodulation) using BPSK (binary phase shift keying), QPSK (quadraturephase shift keying), 16-QAM, 64-QAM, 256-QAM, and/or the like. Physicalradio transmission may be enhanced by dynamically or semi-dynamicallychanging the modulation and coding scheme depending on transmissionrequirements and radio conditions.

FIG. 1 is a diagram depicting example sets of OFDM subcarriers as per anaspect of an embodiment of the present invention. As illustrated in thisexample, arrow(s) in the diagram may depict a subcarrier in amulticarrier OFDM system. The OFDM system may use technology such asOFDM technology, SC-OFDM (single carrier-OFDM) technology, or the like.For example, arrow 101 shows a subcarrier transmitting informationsymbols. FIG. 1 is for illustration purposes, and a typical multicarrierOFDM system may include more subcarriers in a carrier. For example, thenumber of subcarriers in a carrier may be in the range of 10 to 10,000subcarriers. FIG. 1 shows two guard bands 106 and 107 in a transmissionband. As illustrated in FIG. 1, guard band 106 is between subcarriers103 and subcarriers 104. The example set of subcarriers A 102 includessubcarriers 103 and subcarriers 104. FIG. 1 also illustrates an exampleset of subcarriers B 105. As illustrated, there is no guard band betweenany two subcarriers in the example set of subcarriers B 105. Carriers ina multicarrier OFDM communication system may be contiguous carriers,non-contiguous carriers, or a combination of both contiguous andnon-contiguous carriers.

FIG. 2 is a diagram depicting an example transmission time and receptiontime for two carriers as per an aspect of an embodiment of the presentinvention. A multicarrier OFDM communication system may include one ormore carriers, for example, ranging from 1 to 10 carriers. Carrier A 204and carrier B 205 may have the same or different timing structures.Although FIG. 2 shows two synchronized carriers, carrier A 204 andcarrier B 205 may or may not be synchronized with each other. Differentradio frame structures may be supported for FDD (frequency divisionduplex) and TDD (time division duplex) duplex mechanisms. FIG. 2 showsan example FDD frame timing. Downlink and uplink transmissions may beorganized into radio frames 201. In this example, radio frame durationis 10 msec. Other frame durations, for example, in the range of 1 to 100msec may also be supported. In this example, a 10 ms radio frame 201 maybe divided into ten equally sized subframes 202. Other subframedurations such as including 0.5 msec, 1 msec, 2 msec, and 5 msec mayalso be supported. Sub-frame(s) may consist of two or more slots 206.For the example of FDD, 10 subframes may be available for downlinktransmission and 10 subframes may be available for uplink transmissionsin a 10 ms interval. Uplink and downlink transmissions may be separatedin the frequency domain. Slot(s) may include a plurality of OFDM symbols203. The number of OFDM symbols 203 in a slot 206 may depend on thecyclic prefix length and subcarrier spacing.

FIG. 3 is a diagram depicting OFDM radio resources as per an aspect ofan embodiment of the present invention. The resource grid structure intime 304 and frequency 305 is illustrated in FIG. 3. The quantity ofdownlink subcarriers or resource blocks (RB) (in this example 6 to 100RBs) may depend, at least in part, on the downlink transmissionbandwidth 306 configured in the cell. The smallest radio resource unitmay be called a resource element (e.g. 301). Resource elements may begrouped into resource blocks (e.g. 302). Resource blocks may be groupedinto larger radio resources called Resource Block Groups (RBG) (e.g.303). The transmitted signal in slot 206 may be described by one orseveral resource grids of a plurality of subcarriers and a plurality ofOFDM symbols. Resource blocks may be used to describe the mapping ofcertain physical channels to resource elements. Other pre-definedgroupings of physical resource elements may be implemented in the systemdepending on the radio technology. For example, 24 subcarriers may begrouped as a radio block for a duration of 5 msec.

FIG. 4 is an example block diagram of a base station 401 and a wirelessdevice 406, as per an aspect of an embodiment of the present invention.A communication network 400 may include at least one base station 401and at least one wireless device 406. The base station 401 may includeat least one communication interface 402, at least one processor 403,and at least one set of program code instructions 405 stored innon-transitory memory 404 and executable by the at least one processor403. The wireless device 406 may include at least one communicationinterface 407, at least one processor 408, and at least one set ofprogram code instructions 410 stored in non-transitory memory 409 andexecutable by the at least one processor 408. Communication interface402 in base station 401 may be configured to engage in communicationwith communication interface 407 in wireless device 406 via acommunication path that includes at least one wireless link 411.Wireless link 411 may be a bi-directional link. Communication interface407 in wireless device 406 may also be configured to engage in acommunication with communication interface 402 in base station 401. Basestation 401 and wireless device 406 may be configured to send andreceive data over wireless link 411 using multiple frequency carriers.According to some of the various aspects of embodiments, transceiver(s)may be employed. A transceiver is a device that includes both atransmitter and receiver. Transceivers may be employed in devices suchas wireless devices, base stations, relay nodes, and/or the like. Someexample embodiments for radio technology implemented in communicationinterface 402, 407 and wireless link 411 are illustrated in FIG. 1, FIG.2, and FIG. 3, and associated text.

According to some of the various aspects of embodiments, an LTE networkmay include many base stations, providing a user plane (PDCP: packetdata convergence protocol/RLC: radio link control/MAC: media accesscontrol/PHY: physical) and control plane (RRC: radio resource control)protocol terminations towards the wireless device. The base station(s)may be interconnected with other base station(s) by means of an X2interface. The base stations may also be connected by means of an S1interface to an EPC (Evolved Packet Core). For example, the basestations may be interconnected to the MME (Mobility Management Entity)by means of the S1-MME interface and to the Serving Gateway (S-GW) bymeans of the S1-U interface. The S1 interface may support a many-to-manyrelation between MMEs/Serving Gateways and base stations. A base stationmay include many sectors for example: 1, 2, 3, 4, or 6 sectors. A basestation may include many cells, for example, ranging from 1 to 50 cellsor more. A cell may be categorized, for example, as a primary cell orsecondary cell. When carrier aggregation is configured, a wirelessdevice may have one RRC connection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell may providethe NAS (non-access stratum) mobility information (e.g. TAI-trackingarea identifier), and at RRC connection re-establishment/handover, oneserving cell may provide the security input. This cell may be referredto as the Primary Cell (PCell). In the downlink, the carriercorresponding to the PCell may be the Downlink Primary Component Carrier(DL PCC), while in the uplink, it may be the Uplink Primary ComponentCarrier (UL PCC). Depending on wireless device capabilities, SecondaryCells (SCells) may be configured to form together with the PCell a setof serving cells. In the downlink, the carrier corresponding to an SCellmay be a Downlink Secondary Component Carrier (DL SCC), while in theuplink, it may be an Uplink Secondary Component Carrier (UL SCC). AnSCell may or may not have an uplink carrier.

A cell, comprising a downlink carrier and optionally an uplink carrier,is assigned a physical cell ID and a cell index. A carrier (downlink oruplink) may belong to one cell, the cell ID or Cell index may alsoidentify the downlink carrier or uplink carrier of the cell (dependingon the context it is used). In the specification, cell ID may be equallyreferred to a carrier ID, and cell index may be referred to carrierindex. In implementation, the physical cell ID or cell index may beassigned to a cell. Cell ID may be determined using the synchronizationsignal transmitted on a downlink carrier. Cell index may be determinedusing RRC messages. For example, when the specification refers to afirst physical cell ID for a first downlink carrier, it may mean thefirst physical cell ID is for a cell comprising the first downlinkcarrier. The same concept may apply to, for example, carrier activation.When the specification indicates that a first carrier is activated, itequally means that the cell comprising the first carrier is activated.

Embodiments may be configured to operate as needed. The disclosedmechanism may be performed when certain criteria are met, for example,in wireless device, base station, radio environment, network, acombination of the above, and/or the like. Example criteria may bebased, at least in part, on for example, traffic load, initial systemset up, packet sizes, traffic characteristics, a combination of theabove, and/or the like. When the one or more criteria are met, theexample embodiments may be applied. Therefore, it may be possible toimplement example embodiments that selectively implement disclosedprotocols.

In carrier aggregation, two or more carriers may be aggregated in orderto support wider transmission bandwidths. A wireless device maysimultaneously receive or transmit on one or multiple carriers dependingon its capabilities. An LTE Rel-10 or above wireless device withreception and/or transmission capabilities for carrier aggregation maysimultaneously receive and/or transmit on multiple carrierscorresponding to multiple serving cells. An LTE Rel-8/9 wireless devicemay receive on a single carrier and transmit on a single carriercorresponding to one serving cell. Carrier aggregation may be supportedfor both contiguous and non-contiguous carriers. A carrier may comprisea plurality of resource blocks in the frequency domain. A wirelessdevice may be configured to aggregate a different number of carriersoriginating from the same base station and of possibly differentbandwidths in the uplink and the downlink. The number of downlinkcarriers that may be configured may depend, at least in part, on thedownlink aggregation capability of the wireless device. The number ofuplink carriers that may be configured may depend, at least in part, onthe uplink aggregation capability of the wireless device. A wirelessdevice may not be configured with more uplink carriers than downlinkcarriers. In typical TDD deployments, the number of carriers and thebandwidth of a carrier in uplink and downlink may be the same. Carriersoriginating from the same base station may or may not provide the samecoverage.

According to the LTE release 10 standard, carriers should be LTE Rel-8/9compatible. Existing mechanisms (e.g. barring) may be used to avoidRel-8/9 wireless devices to camp on a given carrier. The backwardcompatibility of release 10 carriers may introduce additional overheadand reduce air interface spectral efficiency. To overcome this issue, anew carrier type, called non-prime carrier or non-backward compatiblecarrier in this specification, may be introduced for carrier aggregationto enhance spectral efficiency, improve support for overlapping cellsand increase energy efficiency. Non-prime carriers may not include thesame radio structure as legacy carriers and may not be backwardcompatible. Legacy carriers are sometimes referred to prime carriers inthis specification. A prime carrier (backward compatible carrier) may bedifferent from a primary carrier as defined in LTE release 10. A primecarrier in this specification may be a legacy carrier, for example, acarrier compatible with LTE release 8, 9, or 10. Prime carriers maycomprise primary carriers and secondary carriers as defined in LTErelease 10. In this specification, a prime carrier may be a backwardcompatible carrier and may be a primary carrier or a secondary carrier.

According to some of the various aspects of embodiments, enhancedspectral efficiency may be possible by removing or reducing some legacycontrol signaling and overhead (for example, PSS, SSS, PBCH, SIB, PCH,PDCCH, and/or the like) and/or common reference signal symbols in thedownlink. According to some of the various aspects of embodiments, someof the legacy control signaling overhead may be maintained, for example,PSS/SSS may be transmitted in unsynchronized non-prime carriers.Spectral efficiency in the downlink of non-prime carriers may beimproved. An enhanced PDCCH for a non-prime carrier may be adoptedinstead of legacy PDCCH to improve the spectral efficiency of thedownlink control channel. The enhanced PDCCH may also improve networkperformance in overlapping cells. A non-prime carrier may be implementedwithout legacy PDCCH. Common reference signal overhead may be removed orreduced. The changes in PDCCH and common reference signal may improvenetwork performance in overlapping cells. According to some of thevarious aspects of embodiments, a subframe may become empty or include areduced number of symbols. This may reduce power consumption in the basestation. A base station may be configured to: not transmit any signal ina subframe (for example, enter sleep mode or a power saving mode);and/or reduce power consumption when the base station does not transmitany data packet or control packets in that subframe. In prime carriers,a base station may transmit signals in all subframes, even the almostblank subframes. In a non-prime carrier, there may be at least onesub-frame in which the base station does not transmit any data, control,or reference signals on the non-prime carrier. This mechanism mayenhance energy efficiency in a base station.

According to some of the various aspects of embodiments, a non-primecarrier may be associated with a prime carrier (backward compatiblecarrier). A non-prime carrier may not be configured as a primary carrierand may serve as a secondary carrier. An uplink primary carrier maycontain PUCCH radio resources. The uplink non-prime carrier may beconfigured to operate without PUCCH radio resources. In LTE Rel-10, theprimary cell configuration and PUCCH configuration may be wirelessdevice-specific. In legacy LTE uplink carriers (Release 10 and before),resource blocks at the two ends of an uplink carrier may be allocated toPUCCH radio resources. A non-prime carrier may be configured to operatewithout PUCCH. Resource blocks at the two ends of the uplink carrier maybe available for PUSCH transmission. In another example embodiment, anon-prime carrier may be configured to operate without any uplink randomaccess channel resources. Carriers may be grouped in a carrier group.Uplink transmissions in a group may have its own reference timing. Anon-prime carrier may be grouped with at least a prime carrier, and theuplink timing of a non-prime carrier may be tied to a prime uplinkcarrier in the same group. A downlink synchronization signal in areference cell of the group is employed to synchronize the timing ofcells in a cell group. A group may be configured with a group index.Timing groups in a wireless device may be configured employing RRCconfiguration messages that associate a cell group index to at least onecell identifier/index.

According to some of the various aspects of embodiments, a non-primecarrier may be configured to operate as a synchronous carrier withanother carrier. In another example embodiment, a non-prime carrier mayoperate as an unsynchronized carrier. In synchronized non-primecarriers, the legacy and additional non-prime carriers may besynchronized in time and frequency. A minimum or a reducedsynchronization processing may be needed in the receiver.Synchronization is considered from the perspective of the wirelessdevice receiver. In unsynchronized non-prime carriers, the legacy andadditional carriers may not be synchronized with the same degree ofaccuracy as for the synchronized carriers. In unsynchronized non-primecarriers, the associated legacy and additional carriers may operatewithout being synchronized with the same degree of accuracy as for thesynchronized carriers. Wireless devices may need to performsynchronizfdsation on unsynchronized non-prime carriers. According tosome of the various aspects of embodiments, when a non-prime carrier andthe associated prime carrier are in the same band or have adjacentfrequencies, the two carriers may be considered as synchronized. Inanother example embodiment, when a non-prime carrier and the associatedprime carrier are in two different bands, the two carriers may beconsidered as unsynchronized carriers with respect to the wirelessdevice. According to some of the various aspects of embodiments, an LTEnetwork and/or a wireless device may support synchronized non-primecarriers, unsynchronized non-prime carriers, none of them, or both ofthem. Some wireless devices may be configured to not support any type ofnon-prime carriers. Some wireless devices may support synchronizednon-prime carriers, or unsynchronized non-prime carriers or both.Network overhead and signaling may be implemented differently insynchronized non-prime and unsynchronized non-prime carriers.

According to some of the various aspects of embodiments, a wirelessdevice may need to identify the type of a non-prime carrier before usingthe non-prime carrier. This may be achieved by higher layer signaling(RRC signaling) or a wireless device may detect a carrier type by itself(for example, by autonomous wireless device detection). According tosome of the various aspects of embodiments, a non-prime carrier type maybe configured as an unsynchronized non-prime carrier or as asynchronized non-prime carrier. When a base station configures anon-prime carrier for a wireless device, the wireless device may beinformed of the carrier synchronization type (synchronized orunsynchronized) by the base station. According to some of the variousaspects of embodiments, the wireless device may be informed that aconfigured non-prime carrier is a synchronized carrier. Information toidentify a reference associated carrier for time/frequency tracking of asynchronized carrier may be configured in a wireless device via higherlayer signaling (RRC signaling) or may be decided by grouping carriers.According to some of the various aspects of embodiments, a synchronizednon-prime carrier may be configured to operate without transmittingPSS/SSS. The wireless device may skip further synchronization on thenon-prime carrier and may depend on the associated legacy carrier (primecarrier) timing. In another example embodiment, PSS/SSS may betransmitted in a synchronous non-prime carrier. According to some of thevarious aspects of embodiments, a wireless device may be informed that aconfigured non-prime carrier is an unsynchronized carrier. The wirelessdevice may perform synchronization by detecting PSS/SSS and/or commonreference signal on the non-prime carrier.

According to some of the various aspects of embodiments, in non-primecarriers, the demodulation reference signal may be used for demodulationpurposes. The existing demodulation reference signal patterns may beused on a non-prime carrier. According to some of the various aspects ofembodiments, demodulation reference signal may be punctured if itoverlaps with other signals on the same radio resources. According tosome of the various aspects of embodiments, the common reference signal(common reference signal) may be configured to not be transmitted inevery subframe to reduce common reference signal overhead. In anotherexample embodiment, the common reference signal (common referencesignal) may be configured to not be transmitted at all in a non-backwardcompatible carrier. According to some of the various aspects ofembodiments, a non-prime carrier may carry one reference signal portwithin one subframe with a 5 ms periodicity. For example, one referencesignal port may comprise LTE common reference signal port 0 resourceelements per physical resource block and Rel-8 common reference signalsequence. In some embodiments, common reference signal may not be usedfor demodulation. In a prime carrier, common reference signal spanssubstantially the entire bandwidth of the carrier. In a non-primecarrier, bandwidth of the common reference signal port may be one of:(a) a full carrier bandwidth; (b) the minimum of system bandwidth and X,where X is for example 6 or 25 resource blocks; and (c) configurable(for example by base station transmitting RRC message(s) to wirelessdevice when the carrier is configured) between full system bandwidth andthe minimum of system bandwidth and X. For example, X may be selectedfrom 6 or 25 resource blocks. In a synchronized non-prime carrier,common reference signal overhead may be reduced compared with legacycarriers. For example, common reference signal in a synchronizednon-prime carrier may be the same as common reference signal in anunsynchronized non-prime carrier. In another example embodiment, commonreference signal overhead may be further reduced compared withunsynchronized non-prime carriers or may not be transmitted.

Non-prime carriers may be configured to not support all transmissionmodes. For example, transmission modes 1 to 8 may not be supported on anon-prime carrier, since the radio resource configuration may not becompatible with transmission modes 1 to 8. According to some of thevarious aspects of embodiments, multiple layers of transmissions may besupported on a non-prime carrier. For example, up to eight layertransmission schemes may be supported on a non-prime carrier.

According to some of the various aspects of embodiments, for FDD: SSSand PSS may be transmitted in OFDM symbol 1 and 2, respectively; and maybe transmitted in the first slot of subframe 0 and 5 with normal andextended cyclic prefix. For TDD, the OFDM symbol spacing and orderingbetween SSS and PSS may be the same as Rel-8. According to some of thevarious aspects of embodiments, SSS may precede PSS. There may be twoOFDM symbols between SSS and PSS. The radio resource location of SSS andPSS in time may be different when compared with legacy carriers.

Potential motivations for changing the time/frequency location relativeto LTE Rel-8, may be: preventing acquisition of a new carrier; reducinginter-cell interference; and avoiding demodulation reference signaloverlap in central 6 physical resource blocks. According to some of thevarious aspects of embodiments, the time location of the PSS/SSS in aframe and/or subframe may be changed and the frequency location ofPSS/SSS may not be changed. The PSS/SSS may be transmitted at adifferent location in time in the same or different subframe comparedwith prime carriers. There may be no overlap between PSS/SSS radioresources of a prime carrier and a non-prime carrier operating in thesame frequency. This may reduce PSS/SSS interference in overlappingareas. PSS/SSS configuration, such as the location and/or sequences ofPSS/SSS may be pre-defined or may be communicated to a wireless devicevia higher layer signaling. The wireless device then may acquire thePSS/SSS of a non-prime carrier for time and/or frequencysynchronization.

According to some of the various aspects of embodiments, PSS/SSStransmission on non-prime carriers may collide with demodulationreference signal. Many implementation options may be available toaddress this issue. For example, demodulation reference signal may bepunctured when colliding with PSS/SSS to resolve the collision betweenPSS/SSS and demodulation reference signal. The non-prime carrier may usewireless device-specific reference signal for demodulation. On thelegacy carrier, the wireless device-specific reference signal may beconfigured to not transmit in subframe 0 and subframe 5 in the central 6resource blocks since the PSS/SSS transmitted in these resource blocksoverlaps with the wireless device-specific reference signal locations.The motive for changing the PSS/SSS time locations would be to addressthe case where the PSS/SSS collide with the demodulation referencesignal. According to some of the various aspects of embodiments, LTERel-10 procedure may be employed and the demodulation reference signalmay not be transmitted in the resource blocks where the PSS/SSS aretransmitted. The difference with Rel-10, is that for an additionalcarrier type in Rel-11, common reference signal overhead may be reducedand common reference signal may not to be used for demodulationpurposes. In another example embodiment, the same sequences as release 8may be employed for PSS/SSS and PSS/SSS time locations may be changed.It may be possible to use the same (or similar) cell searcher as used inlegacy carriers (in Rel-8/9/10).

According to some of the various aspects of embodiments, for the cellacquisition/detection of a non-prime carrier, legacydetection/acquisition signals may be employed for a non-prime carrier.New time/frequency configurations of existing signals may beimplemented. For unsynchronized non-prime carriers, Rel-8 PSS/SSSsequences may be transmitted. The time-frequency location of PSS/SSSrelative to Rel-8 may be changed to prevent the acquisition of anon-prime carrier. Inter-cell carrier interference may reduce thereliability of synchronization signals (PSS/SSS) and broadcastinformation (PBCH) between interfering cells (for example between amacro cell and a small cell). A new time location of PSS/SSS may beapplied on a non-prime carrier for interference co-ordinations so thatthe collision of the synchronization signals between interfering cellsmay be reduced or avoided.

According to some of the various aspects of embodiments, a wirelessdevice supporting unsynchronized non-prime carrier may support thefunctionality of performing time/frequency synchronization on thenon-prime carrier using the PSS/SSS transmitted on that non-primecarrier. Implementation of synchronization in a synchronized non-primecarrier may be simpler and a wireless device may obtain synchronizationinformation from the associated prime carrier. According to some of thevarious aspects of embodiments, a synchronized non-prime carrier may beconfigured to operate without PSS/SSS transmission for use in time andfrequency tracking. A wireless device may use the synchronizationobtained from the associated prime carrier. If PSS/SSS are nottransmitted on the synchronized carriers, then demodulation referencesignal puncturing or other solutions for PSS/SSS may not be needed toavoid the collision between PSS/SSS and demodulation reference signal.In another example embodiment, PSS/SSS may be transmitted on asynchronous non-prime carrier. A synchronized reference carrier may be alegacy carrier (prime carrier) synchronized with a synchronizednon-prime carrier in time and/or frequency. In order to obtainsynchronization information of the synchronized non-prime carrier,synchronization information of the synchronization reference carrier maybe employed. The synchronization reference carrier may be configured ina wireless device via higher-layer signaling.

A mechanism may be implemented to prevent a wireless device (forexample, an LTE release 8, 9 or 10 wireless device) from acquiring thePSS/SSS of a non-prime carrier (e.g. during the cell search process).The mechanism may be implemented at the physical layer or at higherlayers. A wireless device may search for the legacy cells and may attachto a cell that transmits the legacy PSS/SSS. The wireless device mayreceive configuration information of carriers that the wireless devicemay employ for communications using carrier aggregation. The carrierconfiguration information may include, for example, FDD/TDDconfiguration, cyclic Prefix type, bandwidth, cell index/ID, uplinkconfiguration, downlink configuration, configuration for physicalchannels, associated prime carrier, cross carrier schedulingconfiguration, a combination of the above, and/or the like.

According to some of the various aspects of embodiments, wirelessdevices may consider the new time location of PSS/SSS radio resources toidentify a non-prime carrier type and not to spend considerableresources on any subsequent procedures after PSS/SSS acquisition (andbefore being barred from further camping on the non-prime type at alater stage). Physical layer procedures may be employed to distinguish aprime carrier from a non-prime carrier. The wireless device may searchfor the prime carriers and may be configured to not look for non-primecarriers. According to some of the various aspects of embodiments, aphysical a new time location of PSS/SSS may not be effective mechanismto bar legacy devices. A wireless device may be able to decode the newPSS (e.g., if the new PSS is identical to the old PSS except a certainsymbol offset), depending on implementation, and the wireless device mayidentify a successful SSS decoding. According to some of the variousaspects of embodiments, physical layer mechanisms may prevent legacywireless devices from acquiring non-prime carriers. In another exampleembodiment, legacy wireless devices may be prevented from acquiringnon-prime carriers by higher layers. If physical layer mechanism doesnot prevent legacy wireless devices from acquiring non-prime carries,wireless devices may be able to detect/acquire the cell of a non-primecarrier and may try to select/reselect a non-prime cell. This maydegrade legacy wireless devices' performance in cellselection/reselection. If PSS/SSS of a non-prime cell is non-visible bylegacy wireless devices and/or is distinguishable by legacy wirelessdevices, legacy wireless devices may not be able to select/reselect thenon-prime cell. This may be a solution for legacy wireless devices, andit may enable Rel-11 wireless devices to differentiate non-primecarriers from prime carriers by PSS/SSS detection.

If a wireless device physical layer does not detect the differencesbetween prime and non-prime carriers, and if legacy wireless devicephysical layer detects/acquires a non-prime carrier, then wirelessdevice may employ higher layer signaling rules to prevent measurement,selecting and/or reselecting a non-prime cell. A wireless device may notbe able to receive higher layer signaling information on a non-primecarrier, for example broadcast control channel. Wireless device behaviorwhen higher level essential information is missing may be triggered andhigher layer signaling may prevent legacy wireless devices fromselecting/reselecting a non-prime cell. The higher layer mechanisms maybe implemented to prevent legacy wireless devices access to non-primecells.

Since non-prime carriers may operate jointly with backward compatiblecarriers (prime carriers) and may only operate in an RRC connectedstate, a wireless device may obtain some RRC information (for example,cell configuration parameters) before accessing non-prime carriers.According to some of the various aspects of embodiments, non-primecarriers may be configured to operate without transmitting PBCH and/orother system information blocks. Paging may be configured to betransmitted on prime carriers, which may include a primary cell for awireless device. Paging may be configured to not transmit on non-primecarriers. Random access responses may be supported only on a primarycarrier. Common control channels may be configured to broadcast on primecarriers. Non-primary carriers may be configured to not broadcast commoncontrol channels. Non-prime carriers may be configured to operatewithout common search space on physical control channel. Common searchspace may be defined exclusively for PDCCH resources in a primarycarrier.

According to some of the various aspects of embodiments, enhanced PDCCHon a non-prime carrier may be supported. Cross-carrier scheduling fromanother carrier, for example the associated prime, carrier may besupported. A cross-carrier scheduling scheme may be implemented forresource allocation on non-prime carriers. Enhanced PDCCH may betransmitted on a non-prime carrier. Non-prime carriers may be configuredto operate without transmitting legacy PDDCH. Cross carrier schedulingfrom another carrier employing a carrier indication field may beconfigured. The usage of enhanced PDCCH and cross carrier scheduling maybe configurable using RRC messages. Enhanced PDCCH configuration of anon-prime carrier may be communicated to a wireless device employing RRCsignaling when the non-prime carrier is configured. Enhanced PDDCHconfiguration parameters may comprise a frequency offset and/orbandwidth in terms of resource blocks. According to some of the variousaspects of embodiments, additional fields such as: the starting symbolof an enhanced PDCCH, the starting symbol of PDSCH, an enhanced PHICHconfiguration, a combination of the above, and/or the like may beconfigured for a non-prime carrier in the wireless device. Theseparameters may be configured via RRC signaling, for example when anon-prime carrier is configured.

A non-prime carrier may be configured to operate without PCFICH. Anenhanced PDCCH configuration may be transmitted to the wireless deviceemploying RRC signaling. When cross carrier scheduling is used, thePHICH for the non-prime uplink carrier may be transmitted on thescheduling downlink carrier. According to some of the various aspects ofembodiments, when enhanced PDCCH on a non-prime carrier is implemented,enhanced PHICH on the non-prime carrier may be configured. Radioresources of enhanced PHICH may employ the resource blocks employed forthe enhanced PDCCH of a non-prime carrier. The enhanced PHICH andenhanced PDCCH on a non-prime carrier may employ different resourceelements if a given resource block. The resource elements may not beshared between enhanced PDCCH and enhanced PHICH. In another exampleembodiment, PHICH may be transmitted on the associated prime carrier.PHICH or enhanced PHICH may be transmitted on a downlink carrier. PHICHor enhanced PHICH for an uplink carrier may carry ack/nack for packetstransmitted on the uplink carrier.

According to some of the various aspects of embodiments, non-primecarriers may be configured to operate without transmitting PBCH, SIBs,paging messages, random access responses, legacy PDCCH, PCFICH, acombination of the above, and/or the like. In another exampleembodiment, some of control channels, for example PBCH, may bemaintained in a non-prime carrier. Common reference signal symbolsoverhead may also be reduced compared with prime carriers.

According to some of the various aspects of embodiments, non-primecarriers may be employed to reduce inter-cell interference. In legacysystems, synchronization signals of different carriers transmitted inthe same frequency may interfere with each other. According to some ofthe various aspects of embodiments, the PSS/SSS of a prime carrier maybe configured to not overlap with PSS/SSS of a non-prime carrier. Inanother example embodiment, synchronized non-prime carriers may beconfigured to operate without transmitting PSS/SSS. This may reduceinterference due to synchronization signals on other downlink carrierstransmitted in the same frequency in the overlapping coverage areas.According to some of the various aspects of embodiments, commonreference signal overhead may be reduced in non-prime downlink carriers.Reduction in common reference signal transmission in non-prime carrierscompared with prime carriers may reduce interference due to commonreference signals on other downlink carriers transmitted in the samefrequency.

According to some of the various aspects of embodiments, the startingsymbol of enhanced PDCCH and/or PDSCH on a non-prime carrier may beconfigurable in all or a subset of subframes of a non-prime carrier. Atleast one RRC reconfiguration message may indicate the configurationparameters of a non-prime carrier to the wireless device, includingenhanced PDCCH and PDSCH configuration parameters and subframes that theconfiguration is applicable. For example, the starting symbol may beconfigured as the first, second, third, or forth symbol in a subset ofsubframes or all subframes. If PDSCH and/or enhanced PDCCH start, forexample, from the third symbol in a subframe, no or a substantiallyreduced signal power may be transmitted in the first and second symbolsof a subframe. The initial symbols (first and second symbols of a subsetor all subframes in this example) on another prime downlink carrieroperating on the same frequency may be employed for transmission ofPDCCH. Such a configuration may reduce inter-cell interference betweencells with an overlapping coverage area operating in the same frequency.A more reliable PDCCH transmission may be achieved. For example, apotential interferer non-prime cell may be configured to not transmit ata high power when another prime cell is transmitting PCFICH/PDCCH/PHICHsymbols in the same cell frequency. In another example embodiment,enhanced PDCCH and PDSCH on a non-prime carrier may start from the firstsymbol to increase physical resources available to enhanced PDCCH andPDSCH of a non-prime carrier. In this configuration, the first symbol ofa frame may be employed for control and data transmission, and basestation may start enhanced PDCCH and PDSCH transmission from the firstsymbol of a frame and end at the last symbol of the subframe.

According to some of the various aspects of embodiments, a non-primecarrier may include enhanced PDCCH resources. Enhanced PDCCH may act asPDCCH for the non-prime carrier. Enhanced PDCCH may carry schedulinginformation for downlink and uplink shared channels and may also carrypower control information for uplink transmissions. Beamforming and/orspecial multiplexing may be employed for enhanced PDCCH. For example,scheduling packets of two different wireless devices may share the sameenhanced PDCCH resources using spatial multiplexing techniques. Anon-prime carrier may not be initially defined for standalone operation.A non-prime carrier may be associated with a backward compatiblecarrier. According to some of the various aspects of embodiments, anon-prime carrier may be contiguously deployed next to the associatedprime carrier. In a non-prime carrier, PDSCH may be scheduledindependently from the other aggregated carriers employing enhancedPDCCH and with independent HARQ processes. PDSCH in a non-prime carriermay be cross-carrier scheduled by the other aggregated carrier.

In case of cross-carrier scheduling in LTE Rel-10 carrier aggregation,the PDSCH of a carrier may be cross carrier scheduled by PDCCH ofanother carrier. The PDSCH starting position of the scheduled carriermay be RRC-signaled to the wireless device. In LTE Rel-10 carrieraggregation, the starting position of PDSCH cannot be configured to bethe first symbol. PCFICH transmission is mandatory, and PDCCH and PHICHshould be configured. PDCCH transmission should be supported in allsubframes. At least transmission of system information blocks and/orother necessary control information may be supported on a carrierwithout employing cross carrier scheduling, and this require PDCCHresources of the carrier. The mandatory configuration of PCFICH, PDCCH,and/or PHICH on carriers including carriers that are cross carrierscheduled may reduce spectral efficiency in release 10 or before LTEcarriers. Furthermore, in legacy systems the starting symbol of PCFICHand PDCCH is not configurable and should always start from the firstsymbol in LTE subframes.

A non-prime carrier may be configured to not transmit enhanced PDCCHand/or PDSCH in its starting OFDM symbol(s) in a subframe. A basestation may configure the starting OFDM symbol(s) in a subframe of anon-prime carrier in order to reduce transmission power in some ofinitial OFDM symbols for the purpose of interference coordination (e.g.scenarios where one cell employs legacy PDCCH and another cell employsenhanced PDCCH). The PDSCH and/or enhanced PDCCH starting position of anon-prime carrier may be transmitted to the wireless device employingRRC messages. A non-prime carrier may be configured to not carry thelegacy PDCCH. The RRC signaling for non-prime carrier configuration mayindicate the very first OFDM symbol in a subframe as the PDSCH startingposition, unlike legacy LTE systems. The enhanced PDCCH startingposition may be the same as the PDSCH starting position. In anotherexample embodiment, the enhanced PDCCH starting position may not be sameas the PDSCH starting position.

Legacy PDCCH may not be present on a non-prime carrier. In this case,the scheduling may be done through at least one of the following twoways: a) cross-carrier scheduling from another carrier (for example, theassociated backward-compatible carrier or another carrier); or b)enhanced PDCCH may be configured on the non-prime carrier so as toimprove control channel capacity and provide interference coordinationon the control channel. Enhanced PDDCH of interfering cells may beconfigured in a way that enhanced PDDCH of interfering cells may notoverlap or may have reduced overlap in radio resources. If cross-carrierscheduling is employed, there may be no need for PHICH and PCFICH on thenon-prime carrier. The HARQ ack/nack feedback may be transmitted on thescheduling carrier. If enhanced PDCCH is used in a non-prime carrier, aPHICH may be implemented for the non-prime carrier.

The enhanced PDCCH radio resources may be configurable. Theconfiguration may comprise at least one of the following: i) a startingfrequency offset in terms of a first number of radio resource blocks;ii) bandwidth of enhanced physical downlink control channel in terms ofa second number of radio resource blocks; iii) starting time in asubframe in terms of number of symbols; iv) ending time in a subframe interms of slots (or symbols); v) beamforming information for the physicaldownlink control channel, and/or vi) a combination of the some of theparameters above. According to some of the various aspects ofembodiments, enhanced PDCCH configuration may be in the form of an arraywhere an element in the array may include the above parameters. EnhancedPDCCH may include many non-overlapping radio resource segments in anon-prime carrier.

Example embodiments of the invention may enable transmission andreception of control and data traffic in a multicarrier OFDMcommunication system. Other example embodiments may comprise anon-transitory tangible computer readable media comprising instructionsexecutable by one or more processors to cause transmission and receptionof control and data traffic in a multicarrier OFDM communicationsystems. Yet other example embodiments may comprise an article ofmanufacture that comprises a non-transitory tangible computer readablemachine-accessible medium having instructions encoded thereon forenabling programmable hardware to cause a device (e.g. wirelesscommunicator, wireless device, base station, etc.) to enabletransmission and reception of control and data traffic in a multicarrierOFDM communication system. The device may include processors, memory,interfaces, and/or the like. Other example embodiments may comprisecommunication networks comprising devices such as base stations,wireless devices (wireless device), servers, switches, antennas, and/orthe like.

FIG. 5 is a diagram depicting example time and frequency resources forprime carrier 601 and non-prime carrier 602 as per an aspect of anembodiment of the present invention. FIG. 6 is a diagram illustratingsynchronization, data and control transmission channels as per an aspectof an embodiment of the present invention. A base station may transmitto at least one wireless device a synchronization signal 615, 606, 608,609 comprising a primary synchronization signal 606, 609 and a secondarysynchronization signal 615, 608 on the prime carrier 601. Thesynchronization signal may indicate a physical cell ID for a cellcomprising the prime carrier 601. The synchronization signal may alsoprovide timing information for the prime carrier 601. Thesynchronization signal may be transmitted employing a plurality ofsubcarriers substantially in the center of the frequency band of theprime carrier 601 on the first and sixth subframes (subframe 0 and 5) ofa frame in the plurality of frames. Primary and secondarysynchronization signals may occupy a bandwidth of approximately sixresource blocks. The base station may broadcast to at least one wirelessdevice physical broadcast channel (PBCH) 607 in slot one 604 of subframe0 of the prime carrier 301. At least one wireless device may receive thesynchronization signals to obtain and/or track carrier frame andsubframe timing. At least one wireless device may receive PBCH signal toobtain at least one configuration parameter of the downlink carrier.

According to some of the various aspects of embodiments, a base stationmay transmit a first synchronization signal 615, 606, 608, 609comprising a primary synchronization signal 606, 609 and a secondarysynchronization signal 615, 608 on the prime carrier 601. The firstsynchronization signal may indicate a physical cell ID for a cellcomprising the prime carrier 601. The first synchronization signal mayprovide timing information for the prime carrier 601. A secondsynchronization signal may be transmitted on the non-prime carrier. Thesecond synchronization signal may be transmitted employing a pluralityof subcarriers substantially in the center of the frequency band of thenon-prime carrier 602 employing six resource blocks. A secondsynchronization signal may comprise a second primary synchronizationsignal and a second secondary synchronization signal. According to someof the various aspects of embodiments, the second synchronization signalmay be transmitted on a second time location (different from timelocation of the first synchronization signal) in the same or differentsubframe compared with the first synchronization signal. The secondsynchronization signal may provide timing information for the non-primecarrier 602. In another example embodiment, a non-prime carrier maycarry synchronization signal in resources 610, 611, 613, and 614 similarto prime carriers.

The base station may transmit to at least one wireless device a firstplurality of data packets on a first data channel 703 of the primecarrier 601 on a first plurality of OFDM subcarriers. A first pluralityof OFDM subcarriers may exclude a plurality of subcarriers used fortransmission of the primary 606, 609 and secondary 615, 608synchronization signals in the first and sixth subframes in theplurality of frames. A first plurality of OFDM subcarriers may exclude aplurality of subcarriers used for transmission of the PBCH 607.PSS/SSS/PBCH resources 709 on the prime carrier 601 in an examplesubframe 708 are illustrated in FIG. 6.

The base station may transmit a first plurality of broadcast systeminformation messages (SIB messages) on the first data channel 703employing, for example, radio resources 704. The plurality of broadcastsystem information messages may comprise a plurality of radio linkconfiguration parameters of the prime carrier 601 for a wireless devicereceiving the prime carrier 601 and the non-prime carrier 602 signals.An example radio resource 704 employed for SIB message transmission isillustrated in FIG. 6. SIB messages may be transmitted continuously andmay be transmitted on a subset of the downlink subframes of the primecarrier 601. System information of the non-prime carrier 602 may bereceived via at least one unicast RRC message when the non-prime carrier602 is configured by higher layers. According to some of the variousaspects of embodiments, the at least one unicast RRC message may betransmitted on the first data channel 703 of the prime carrier 601. Thenon-prime carrier 602 may be configured to operate without broadcastingthe system information blocks on the non-prime carrier 602. The basestation may transmit a second plurality of data packets on a second datachannel 705 on a second plurality of OFDM subcarriers of the non-primecarrier 602.

According to some of the various aspects of embodiments, the secondplurality of OFDM subcarriers of the non-prime carrier 602 may comprisethe OFDM subcarriers substantially in the center of the frequency bandat symbols 610, 611, 613, and 614 of the non-prime carrier 602 in thefirst and sixth subframes in the plurality of frames. No primarysynchronization signal and no secondary synchronization signal may betransmitted on the second carrier in radio resource 610, 611, 613, and614. The non-prime carrier may be configured to operate withouttransmitting primary synchronization signal and secondarysynchronization signal in radio resource 610, 611, 613, and 614. Nobroadcast system information message (SIB messages) may be transmittedon the second data channel 705. The non-prime carrier 602 may beconfigured to operate without transmitting or broadcasting systeminformation message (SIB messages). No physical broadcast channel may betransmitted in radio resource 612. The non-prime carrier 602 may beconfigured to operate without transmitting physical broadcast channel inradio resource 612. According to some of the various aspects ofembodiments, if non-prime carrier 602 is a synchronized non-primecarrier, subframe timing of the non-prime carrier 602 may be provided bythe synchronization signal transmitted on the prime carrier 601. Inanother example embodiment, if the non-prime carrier 602 is anunsynchronized non-prime carrier, subframe timing of the non-primecarrier 602 may be provided by a second synchronization signaltransmitted on the non-prime carrier 602. According to some of thevarious aspects of embodiments, if synchronization signals aretransmitted on a non-prime carrier 602, radio resources 712 ofsynchronization signal may be in a different time location in the samesubframe 708 (as shown in FIG. 6) or in a different subframe (not shownin the figure).

The first plurality of data packets and the second plurality of datapackets may be transmitted using a plurality of physical resourceblocks. A physical resource block may comprise reference signal symbolsand data symbols. The broadcast system information messages may be RRCsystem information blocks (SIBs). The radio link configurationinformation may comprise measurement configuration, uplink channelconfiguration, handover parameters, and/or the like.

The primary synchronization signal 606, 609 may be generated using afrequency-domain Zadoff-Chu sequence. The primary synchronization signal606, 609 may be mapped to the last OFDM symbol in slots zero 603 and ten605 for an FDD frame structure. The primary synchronization signal 606,609 may be mapped to the third OFDM symbol in subframes 1 and 6 for theTDD frame structure. The secondary synchronization signal 615, 608 maybe generated employing an interleaved concatenation of two 31 bit binarysequences. The concatenated sequence may be scrambled with a scramblingsequence given by the primary synchronization signal 606, 609. Theportion of the secondary synchronization signal transmitted in subframezero 615 may be different from the portion of the secondarysynchronization signal transmitted in subframe five 608. If a non-primecarrier is configured to transmit synchronization signals, thesynchronization signals transmitted on a prime carrier and thesynchronization signals transmitted on the non-prime carrier may beselected from the same set of available sequences.

According to some of the various aspects of embodiments, downlinkcontrol information may be transmitted on a physical control channel 702on the prime carrier 601. The base station may transmit at least onecontrol message on the first data channel 703. The at least one controlmessage may be configured to cause configuration of a non-prime carrier602 in a wireless device. The at least one control message may comprisethe configuration of radio resources of the non-prime carrier comprisinga second data channel. In a first carrier configuration, the controlchannel 702 may be configured to provide transmission format andscheduling information for the first plurality of data packetstransmitted on the prime carrier 601 and the second plurality of datapackets transmitted on the non-prime carrier 602. The control channel702 may be transmitted on the prime carrier 601 starting from the firstOFDM symbol of a subframe. The control channel may be a physicaldownlink control channel. No physical control format indicator channels,no physical downlink HARQ indicator channel, and no physical downlinkcontrol channels may be transmitted on the non-prime carrier 602. Thenon-prime carrier 602 may be configured to operate without transmittingphysical control format indicator channel, physical downlink HARQindicator channel, and physical downlink control channel. Radioresources of the second data channel 705 may be configured to start fromthe first OFDM symbol of a subframe 708 of the non-prime carrier 602 andto end at the last OFDM symbol of the subframe of the non-prime carrier602. No HARQ feedback may be transmitted on the non-prime carrier 602.The non-prime carrier 602 may be configured to operate withouttransmitting HARQ feedback on the non-prime carrier 602.

FIG. 8 is a diagram depicting example control and data transmission fora prime downlink carrier 601, a non-prime downlink carrier 602, a primeuplink carrier 811, and a non-prime uplink carrier 812 as per an aspectof an embodiment of the present invention. Downlink subframe 903 may notbe transmitted at the same time with uplink subframe 904. Radioresources 905 are employed for transmission of PCFICH, PDCCH, and PHICH.The downlink control channel (PDCCH) in radio resources 905 may beconfigured to provide transmission format and scheduling information fora first plurality of packets transmitted on a first downlink sharedchannel 906, a second plurality of packets transmitted on a seconddownlink shared channel 907, a third plurality of data packetstransmitted on a first uplink shared channel 908, and a fourth pluralityof data packets transmitted on a second uplink shared channel 909. Forexample control packet 916 may provide transmission format andscheduling information for data packet 913. Control packet 922 mayprovide transmission format and scheduling information for data packet933. Control packet 918 may provide transmission format and schedulinginformation for data packet 914. Control packet 920 may providetransmission format and scheduling information for data packet 924.Control packets 918 and 920 may also comprise power control informationfor transmission of packets 914 and 924 respectively. The prime uplinkcarrier 811 may comprise: a) a first portion of bandwidth employed forthe first uplink data channel 908; and b) a second portion of thebandwidth employed for a first uplink control channel 910.

According to some of the various aspects of embodiments, in a secondcarrier configuration, the control channel 702 may be configured toprovide transmission format and scheduling information for the firstplurality of data packets transmitted on the prime carrier 601. Thecontrol channel 702 may be transmitted on the prime carrier 601 startingfrom the first OFDM symbol of a subframe 708. The control channel may bea physical downlink control channel. Second control information may betransmitted on a second control channel 711 on the non-prime carrier602. The second control channel 711 may be configured to providetransmission format and scheduling information for the second pluralityof data packets transmitted on the non-prime carrier 602. The secondcontrol channel may be an enhanced physical downlink control channel.Radio resources of the second data channel 705 may be configured tostart from the first OFDM symbol of a subframe of the non-prime carrier602 and end at the last OFDM symbol of the subframe of the non-primecarrier 602.

FIG. 7 is a diagram depicting example control and data transmission fora prime downlink carrier 601, a non-prime downlink carrier 602, a primeuplink carrier 811, and a non-prime uplink carrier 812 as per an aspectof an embodiment of the present invention. Downlink subframe 803 may notbe transmitted at the same time with uplink subframe 804. Radioresources 805 are employed for transmission of PCFICH, PDCCH, and PHICH.The downlink control channel (PDCCH) in radio resources 805 may beconfigured to provide transmission format and scheduling information fora first plurality of packets transmitted on a first downlink sharedchannel 806, and a third plurality of data packets transmitted on afirst uplink shared channel 808. Enhance control channel 824 may beconfigured to provide transmission format and scheduling information fora second plurality of packets transmitted on a second downlink sharedchannel 807, and a fourth plurality of data packets transmitted on asecond uplink shared channel 809. For example control packet 814 mayprovide transmission format and scheduling information for data packet820. Control packet 816 may provide transmission format and schedulinginformation for data packet 830. Control packet 826 may providetransmission format and scheduling information for data packet 818.Control packet 828 may provide transmission format and schedulinginformation for data packet 832. Control packets 816 and 928 may alsocomprise power control information for transmission of packets 830 and832 respectively. The prime uplink carrier 811 may comprise: a) a firstportion of bandwidth employed for the first uplink data channel 808; andb) a second portion of the bandwidth employed for a first uplink controlchannel 810.

FIG. 7 and FIG. 8 illustrate two example carrier configurations. Carrierconfigurations are wireless device specific. A first wireless deviceconnected to a base station may be configured with a first carrierconfiguration and a second wireless device connected to the same basestation may be configured with a second carrier configuration.Therefore, a base station may provide both first and the secondconfigurations. For a first wireless device the base station may employcross carrier scheduling as shown in FIG. 8, and for a second wirelessdevice the base station may employ enhanced PDCCH as shown in FIG. 8. Abase station may support both configurations in parallel, a firstconfiguration may be applied to a first wireless device, and a secondconfiguration may be applied to a second wireless device. For the firstwireless device, the PDCCH in radio resource 905 may be configured toprovide transmission format and scheduling information for a firstplurality of packets transmitted on a first downlink shared channel 906,a second plurality of packets transmitted on a second downlink sharedchannel 907, a third plurality of data packets transmitted on a firstuplink shared channel 908, and a fourth plurality of data packetstransmitted on a second uplink shared channel 909. During the sameperiod, the downlink control channel (PDCCH) in radio resources 805 maybe configured to provide transmission format and scheduling informationfor a first plurality of packets transmitted on a first downlink sharedchannel 806, and a third plurality of data packets transmitted on afirst uplink shared channel 808. Enhance control channel 824 may beconfigured to provide transmission format and scheduling information fora second plurality of packets transmitted on a second downlink sharedchannel 807, and a fourth plurality of data packets transmitted on asecond uplink shared channel 809.

According to some of the various aspects of embodiments, in a thirdcarrier configuration, the control channel 702 may be configured toprovide transmission format and scheduling information for the firstplurality of data packets transmitted on the prime carrier 601 and thesecond plurality of data packets transmitted on the non-prime carrier602. The control channel 702 may be transmitted on the prime carrier 601starting from the first OFDM symbol of a subframe. The control channelmay be a physical downlink control channel. No physical control formatindicator channels, no physical downlink HARQ indicator channel, and nophysical downlink control channels may be transmitted on the non-primecarrier 602. The non-prime carrier 602 may be configured to operatewithout transmitting physical control format indicator channel, physicaldownlink HARQ indicator channel, and physical downlink control channel.No HARQ feedback may be transmitted on the non-prime carrier 602. Thenon-prime carrier 602 may be configured to operate without transmittingHARQ feedback on the non-prime carrier 602. The starting symbol of radioresources of the second physical downlink shared channel 705 may beindicated by at least one control message. For example, the startingsymbol of the second physical downlink shared channel 705 may beconfigured to start from the third symbol of a subframe. In thisconfiguration, the first and second symbol of the subframe may not beemployed for transmission of control and data channels. The base stationmay transmit substantially reduced power or no power in the first twosymbols of the subframe. In an implementation option, the ending symbolof the second physical downlink shared channel 705 may be indicated byat least one control message.

According to some of the various aspects of embodiments, in a fourthcarrier configuration, the control channel 702 may be configured toprovide transmission format and scheduling information for the firstplurality of data packets transmitted on the prime carrier 601. Thecontrol channel 702 may be transmitted on the prime carrier 601 startingfrom the first OFDM symbol of a subframe 708. The control channel may bea physical downlink control channel. Second control information may betransmitted on a second control channel 711 on the non-prime carrier602. The second control channel 711 may be configured to providetransmission format and scheduling information for the second pluralityof data packets transmitted on the non-prime carrier 602. The secondcontrol channel may be an enhanced physical downlink control channel.The starting symbol of radio resources of the second physical downlinkshared channel 705 and/or the second control channel 711 may beindicated by at least one control message. For example, the startingsymbol of the second physical downlink shared channel 705 and/or thesecond control channel 711 may be configured to start from the thirdsymbol of a subframe. In this configuration, the first and second symbolof the subframe may not be employed for transmission of control and datachannels. The base station may transmit substantially reduced power orno power in the first two symbols of the subframe. In an implementationoption, the ending symbol of the second physical downlink shared channel705 and/or the second control channel 711 may be indicated by at leastone control message.

Radio resources 709 may be configured to provide a synchronizationsignal on the prime carrier 601. In an example carrier configuration, ifthe non-prime carrier is configured to carry a synchronization signal,radio resources 712 may be configured to provide the secondsynchronization signal on the non-prime carrier. In another exampleembodiment, the non-prime carrier may be configured to operate withouttransmitting the second synchronization signal. In that case, a wirelessdevice may employ the synchronization signal 709 transmitted on theprime carrier 601 for frame and subframe timing of the prime carrier 601and the non-prime carrier 602.

As shown in FIG. 6, radio resources employed by enhanced PDCCH may beconfigured to span in a limited number of configured resource blocksstarting from an offset frequency configured in terms of the resourceblocks. PCFICH may not be transmitted on a non-prime carrier, andenhanced PDCCH configuration may be transmitted to the wireless devicevia RRC messages transmitted on a prime carrier. Radio resourcesemployed for PDSCH may span the entire active prime carrier bandwidth infrequency excluding the resource blocks employed by enhanced PDCCH.According to some of the various aspects of embodiments, ifsynchronization signal and/or PBCH are transmitted in a subframe, PDSCHresources may exclude the resource blocks 712 employed bysynchronization signal and/or PBCH in the subframe. According to some ofthe various aspects of embodiments, enhanced PDCCH 711 and PDSCH 705radio resources may start from the first symbol of a subframe and end atthe last symbol of the subframe. Enhanced PDCCH 711 and PDSCH 705 radioresources may span the entire duration of a subframe in time. In anotherexample implementation, the starting symbol and/or the ending symbol ofenhanced PDCCH and PDSCH in all or a subset of subframes may be aconfigurable parameter and may be indicated to a wireless deviceemploying RRC signaling. In an example implementation, some of theresource elements of resource blocks employed for enhanced PDCCH may beemployed for an enhanced PHICH transmission. Enhanced PHICH may carryack/nack for uplink packets transmitted on the non-prime uplink carrier.A control packet transmitted on enhanced PDCCH may employ a subset ofresources allocated to enhanced PDCCH. A packet transmitted on PDSCH mayemploy a subset of resources allocated to PDSCH.

The first plurality of data packets and the second plurality of datapackets may be encrypted packets. The first plurality of data packetsand the second plurality of data packets may be assigned to a radiobearer. A first plurality of packets that are assigned to the same radiobearer may be encrypted using an encryption key and at least oneparameter that changes substantially rapidly over time. An example ofthe parameter that changes substantially rapidly over time may be acounter, for example, a packet sequence number.

RRC messages may be encrypted and may be protected by an integrityheader before it is transmitted. The at least one control message may betransmitted by an RRC protocol module. The at least one control messagemay further comprise configuration information for physical channels fora wireless device. The at least one control message may set up or modifyat least one radio bearer. The at least one control message may modifyconfiguration of at least one parameter of a MAC layer or a physicallayer. The at least one control message may be an RRC connectionreconfiguration message.

The transmission and reception mechanisms in the example embodiments mayincrease bandwidth efficiency in the system. The proposed transmissionand reception mechanisms may provide a set of constraints for assigningwireless physical resources to data and control packet transmission thatmay result in increased overall air interface capacity. The non-primecarrier may be employed to provide additional capacity. In the exampleembodiments, the non-prime carrier may not carry some of the physicalchannels that are required, for example, in LTE release 8, 9 and 10.This may improve wireless interface spectral efficiency.

In an example embodiment of the invention implemented in an LTE network,the first control channel may be a physical control format indicatorchannel (PCFICH), the second control channel may be a physical downlinkcontrol channel (PDCCH), and the first and second data channels may bethe first and second physical downlink shared channels (PDSCH). DownlinkHARQ feedback may be transmitted employing a physical HARQ indicatorchannel (PHICH), and the physical broadcast channel may comprise atleast one information field related to system information.

According to some of the various aspects of embodiments, PCFICH, PDCCH,PBCH, BCCH, and/or PCH may be transmitted on the prime carrier. Thenon-prime carrier may be configured to operate without transmittingPCFICH, PDCCH, PBCH, BCCH and/or PCH in any subframe. PDCCH transmittedon the prime carrier may transmit scheduling packets for the first andsecond PDSCH. An example embodiment may eliminate PCFICH and PDCCHtransmission on the non-prime carrier and release the capacity thatshould have been used for these control channels to PDSCH. This mayincrease the data capacity of the second carrier, and may increase thespectral efficiency of the system. According to some of the variousaspects of embodiments, a carrier in the plurality of carriers may beclassified as a prime carrier or a non-prime carrier, wherein thetransmitter transmits at least one prime carrier and at least onenon-prime carrier. The prime carriers may transmit PCFICH, PDCCH, PBCH,BCCH, PCH channels, and/or the like. The non-prime carriers may beconfigured to operate without transmitting the PCFICH, PDCCH, SS, PBCH,BCCH, PCH channels, and/or the like. The scheduling packetscorresponding to data packets transmitted on non-prime carriers may betransmitted in PDCCH channels of one of the prime carriers. Theresources allocated to the data channel in non-prime carriers may startfrom the first symbol of a subframe.

According to some of the various aspects of embodiments, a wirelessdevice may receive from a base station a synchronization signal 615,606, 608, 609 comprising a primary synchronization signal 606, 609 and asecondary synchronization signal 615, 608 on the prime carrier 601. Thesynchronization signal may indicate a physical cell ID for a cellcomprising the prime carrier 601. The synchronization signal may alsoprovide timing information for the prime carrier 601 and the non-primecarrier 602 in the plurality of carriers. The synchronization signal maybe received employing a plurality of subcarriers substantially in thecenter of the frequency band of the prime carrier 601 on the first andsixth subframes (subframe 0 and 5) of each frame in the plurality offrames. Primary and secondary synchronization signals may occupy abandwidth equal to six resource blocks. The wireless device may receivea physical broadcast channel (PBCH) 607 in slot one 604 of subframe 0 ofthe prime carrier 301. In one example embodiment, radio resources 610,611, 612, 613 and 614 may not be employed for reception of asynchronization signal and PBCH. These resources may be employed forreceiving data on the downlink carrier. For example, these radioresources may be employed for reception of data packets on a non-primecarrier physical downlink shared channel.

According to some of the various aspects of embodiments, a wirelessdevice may receive a first synchronization signal 615, 606, 608, 609comprising a primary synchronization signal 606, 609 and a secondarysynchronization signal 615, 608 on the prime carrier 601. The firstsynchronization signal may indicate a physical cell ID for a cellcomprising the prime carrier 601. The first synchronization signal mayprovide timing information for the prime carrier 601. A secondsynchronization signal may be received on the non-prime carrier. Thesecond synchronization signal may be received employing a plurality ofsubcarriers substantially in the center of the frequency band of thenon-prime carrier 602 employing six resource blocks. A secondsynchronization signal may comprise a second primary synchronizationsignal and a second secondary synchronization signal. According to someof the various aspects of embodiments, the second synchronization signalmay be received on a second time location (different from time locationof the first synchronization signal) in the same or different subframecompared with the first synchronization signal. The secondsynchronization signal may provide timing information for the non-primecarrier 602.

The wireless device may receive from the base station a first pluralityof data packets on a first data channel 703 of the prime carrier 601 ona first plurality of OFDM subcarriers. A first plurality of OFDMsubcarriers may exclude a plurality of subcarriers used for transmissionof the primary 606, 609 and secondary 615, 608 synchronization signalsin the first and sixth subframes in the plurality of frames. A firstplurality of OFDM subcarriers may exclude a plurality of subcarriersused for transmission of the PBCH 607. PSS/SSS/PBCH resources 709 on theprime carrier 601 in an example subframe 708 are illustrated in FIG. 6.

The wireless device may receive from the base station a first pluralityof broadcast system information messages (SIB messages) on the firstdata channel 703 employing, for example, radio resources 704. Theplurality of broadcast system information messages may comprise aplurality of radio link configuration parameters of the prime carrier601 for the wireless device receiving the prime carrier 601 and thenon-prime carrier 602 signals. An example radio resource 704 employedfor SIB message transmission is illustrated in FIG. 6. SIB messages maybe received continuously and may be received on a subset of the downlinksubframes of the prime carrier 601. System information of the non-primecarrier 602 may be received via at least one unicast RRC message whenthe non-prime carrier 602 is configured by higher layers. According tosome of the various aspects of embodiments, the at least one unicast RRCmessage may be received on the first data channel 703 of the primecarrier 601. The non-prime carrier 602 may be configured to operatewithout broadcasting the system information blocks on the non-primecarrier 602. The wireless device may receive a second plurality of datapackets on a second data channel 705 on a second plurality of OFDMsubcarriers of the non-prime carrier 602.

According to some of the various aspects of embodiments, the secondplurality of OFDM subcarriers of the non-prime carrier 602 may comprisethe OFDM subcarriers substantially in the center of the frequency bandat symbols 610, 611, 613, and 614 of the non-prime carrier 602 in thefirst and sixth subframes in the plurality of frames. No primarysynchronization signal and no secondary synchronization signal may bereceived on the second carrier in radio resource 610, 611, 613, and 614.The non-prime carrier may be configured to operate without receivingprimary synchronization signal and secondary synchronization signal inradio resource 610, 611, 613, and 614. No broadcast system informationmessage (SIB messages) may be received on the second data channel 705.The non-prime carrier 602 may be configured to operate without receivingsystem information message (SIB messages). No physical broadcast channelmay be received in radio resource 612. The non-prime carrier 602 may beconfigured to operate without receiving physical broadcast channel inradio resource 612. According to some of the various aspects ofembodiments, if non-prime carrier 602 is a synchronized non-primecarrier, subframe timing of the non-prime carrier 602 may be provided bythe synchronization signal received on the prime carrier 601. In anotherexample embodiment, if the non-prime carrier 602 is an unsynchronizednon-prime carrier, subframe timing of the non-prime carrier 602 may beprovided by a second synchronization signal received on the non-primecarrier 602. According to some of the various aspects of embodiments, ifsynchronization signals are received on a non-prime carrier 602, radioresources 712 of synchronization signal may be in a different timelocation in the same subframe 708 (as shown in FIG. 6) or in a differentsubframe (not shown in FIG. 6). The first plurality of data packets andthe second plurality of data packets may be received using a pluralityof physical resource blocks.

Legacy release 8 and 9 LTE wireless devices may be able to connect to aprime carrier 601. Legacy release 8 and 9 LTE wireless devices may notbe able to connect to non-prime carriers. Wireless devices employing anexample embodiment may be able to connect to a prime carrier 601, andthen employ a non-prime carrier 602 to further enhance the datatransmission rate. The initial connection may be set up employing aprime carrier. A wireless device may receive a paging message on a primecarrier. A wireless device may start a random access procedure in theuplink carrier corresponding to a prime downlink carrier to establish aconnection. Signaling radio bearer one in LTE may be established using aprime downlink carrier and a corresponding prime uplink carrier. Thewireless device may establish other signaling and data radio bearers ona prime carrier, a non-prime carrier, and/or both.

According to some of the various aspects of embodiments, a base stationmay transmit in a frame in the sequential series of frames on a primecarrier the n most significant bits of a system frame number. The basestation may transmit the n most significant bits of a system framenumber employing a plurality of subcarriers substantially in the centerof the frequency band of the prime carrier on the first subframe of theframe in an information element in a control block transmitted on aphysical broadcast channel. Each frame in the sequential series offrames may be assigned a system frame number. The system frame numbermay be represented by m bits. The base station may transmit the (m-n)least significant bits of the system frame number implicitly by encodingcontrol blocks in the physical broadcast channel over 2 (m-n) frames (2to the power of m-n). Sequential position of the encoded control blocksmay determine the (m-n) least significant bits. In other word, thetiming of the encoded control blocks on the physical broadcast channelmay determine the m-n least significant bits. The base station maytransmit the same system frame number in frames of the at least oneprime carrier if the frames are transmitted at the same time.

The base station may transmit and receive, by employing a communicationinterface, a first plurality of packets in the frame on a prime carrier.The communication interface may employ, at least in part, the systemframe number transmitted in the frame of the prime carrier. The primecarrier may be configured to operate broadcasting the system framenumber on the prime carrier. The base station may transmit and receive,by employing a communication interface, a second plurality of packets inthe frame on a non-prime carrier. The communication interface mayemploy, at least in part, the system frame number transmitted in theframe of the prime carrier. The non-prime carrier may be configured tooperate without broadcasting the system frame number on the non-primecarrier.

The physical broadcast channel received on a prime carrier may comprisedownlink bandwidth, system frame number, and/or PHICH configuration ofthe prime carrier. According to some of the various aspects ofembodiments, n may be equal to 8, and m may be equal to 10.

The wireless device may descramble the control blocks received on thephysical broadcast channel with a cell-specific sequence prior tomodulation. The wireless device may demodulate the control blocksreceived on the physical broadcast channel using QPSK modulation. Thewireless device may decode the control blocks transmitted on thephysical broadcast channel employing tail biting convolutional decoding.The receiver may remove CRC bits from a decoded control block of thephysical broadcast channel. The CRC bits may be descrambled according tothe base station transmit antenna configuration. The wireless device mayreceive a plurality of control packets on the second data channel.Integrity checksum may be calculated for the plurality of controlpackets using a plurality of parameters comprising a hyper frame number.

According to some of the various aspects of embodiments, downlinkassignments transmitted on the PDCCH may indicate if there is atransmission on a downlink shared channel for a particular wirelessdevice and/or may provide the relevant hybrid ARQ information. Forconfigured downlink assignments, the hybrid ARQ process identifierassociated with the subframe may be derived, at least in part, as afunction of transmission time interval number. The transmission timeinterval number may be derived as (system framenumber.times.10)+subframe number. When a wireless device needs to readbroadcast control channel, the wireless device may employ the systemframe number for decoding.

FIG. 9 is an example flow chart for configuration of non-backwardcompatible carriers as per an aspect of an embodiment of the presentinvention. According to some of the various aspects of embodiments, abase station may transmit at least one control message to a wirelessdevice (as shown in 950). The at least one control message may comprisean identifier for each carrier in a plurality of carriers andinformation identifying a carrier type for each carrier in the pluralityof carriers. The base station may include other carriers besides theplurality of carriers. The carriers that are not configured using themethod described here may not be considered as a subset of the pluralityof carriers. For example, the base station may include second carriersemploying different technologies not compatible with the disclosedmethod. The second carriers may not be considered a subset of theplurality of carriers. The plurality of carriers may comprise at leastone backward compatible carrier and at least one non-backward compatiblecarrier. The carrier type may be one of backward compatible carrier typeand non-backward compatible carrier type. The first base station maytransmit a plurality of packets to the wireless device on the at leastone non-backward compatible carrier and the at least one backwardcompatible carrier. FIG. 5, FIG. 6, FIG. 7 and FIG. 8 illustrate someexamples of a backward compatible carrier (equally called a primecarrier) and a non-backward compatible carrier (equally called anon-prime carrier).

According to some of the various aspects of embodiments, a first commonreference signal overhead of each of the at least one non-backwardcompatible carrier may be substantially lower than a second commonreference signal overhead of each of the at least one backwardcompatible carrier. For example, backward compatible carriers maytransmit common reference signal only in a limited region of OFDMresources, for example in a limited frequency band, or a part of asubframe. Other embodiments, for example, transmitting common referencesignals only on a subset of subframes may be implemented. In anotherexample, the first common reference signal overhead may be substantiallylower than the second common reference signal overhead at least in someof the subframes. The term substantially lower implies that thenon-backward compatible carriers are designed and operate having a lowercommon reference signal overhead to increase spectral efficiency.

The at least one control message may further comprise informationassociating each of the at least one non-backward compatible carrierwith one of the at least one backward compatible carrier. The basestation may transmit a plurality of control messages to the wirelessdevice on a backward compatible carrier as shown in 954. The pluralityof control messages may comprise scheduling information for transmissionof packets on a non-backward compatible carrier associated with thebackward compatible carrier. The plurality of control messages may bePDCCH control messages. The base station may transmit a plurality ofpackets to the wireless device on the non-backward compatible carrieraccording to the scheduling information as shown in 956. The basestation may receive channel state information of one of the at least onenon-backward compatible carrier from the wireless device on an uplinkcarrier of one of the at least one backward compatible carrier as shownin 952. Channel state information may be received for carriers that areactivated. Base station may not receive channel state information forinactive carriers to reduce uplink overhead and/or wireless deviceprocessing requirements. Scheduling information is includes modulationand coding information, which is configured at least in part based onchannel state information received from the base station.

According to some of the various aspects of embodiments, a wirelessdevice may receive at least one control message from a first basestation. The at least one control message may comprise an identifier foreach carrier in the plurality of carriers and information identifying acarrier type for each carrier in the plurality of carriers. Theplurality of carriers may comprise at least one backward compatiblecarrier, and at least one non-backward compatible carrier. The carriertype may be one of backward compatible carrier type and non-backwardcompatible carrier type. The wireless device may receive a plurality ofpackets from the first base station on the at least one non-backwardcompatible carrier and the at least one backward compatible carrier.

According to some of the various aspects of embodiments, the wirelessdevice may receive a plurality of control messages from the first basestation on a backward compatible carrier. The plurality of controlmessages may comprise scheduling information for reception and/ortransmission of packets on a non-backward compatible carrier associatedwith the backward compatible carrier. The wireless device may receiveand/or transmit a plurality of packets from/to the first base station onthe non-backward compatible carrier according to the schedulinginformation.

According to some of the various aspects of embodiments, the wirelessdevice may transmit channel state information of one of the at least onenon-backward compatible carrier to the first base station on an uplinkcarrier of one of the at least one backward compatible carrier. In anexample implementation, the one non-backward compatible carrier may beassociated with the one backward compatible carrier. Channel stateinformation may be transmitted only for activated carriers.

According to some of the various aspects of embodiments, the controlmessage may be encrypted and may be protected by an integrity headerbefore it is transmitted. The control message may be transmitted byemploying RRC protocol. The control message may further includeconfiguration information for physical channels for the wireless device.The control message may set up or modify at least one radio bearer. Thecontrol message may modify configuration of at least one parameter of aMAC layer or a physical layer. The control message may configure atleast one of a physical layer parameter, a MAC layer parameter and anRLC layer parameter. The control message may be an RRC connectionreconfiguration message. Broadcast system information messages may bebroadcasted on at least one of the at least one backward compatiblecarrier. The control message comprises radio link configurationinformation comprising measurement configuration. The control messagemay comprise radio link configuration information comprising uplinkchannel configuration. The control message may comprise radio linkconfiguration information comprising handover parameters.

According to some of the various aspects of embodiments, the basestation may receive an RRC reconfiguration complete message from thewireless device. The RRC reconfiguration complete message may indicatethat the control message is successfully processed by the wirelessdevice. The RRC reconfiguration complete message may include an RRCtransaction identifier. The RRC reconfiguration message and RRCreconfiguration complete message may be encrypted and may be protectedby an integrity header before being transmitted. The control message maybe an RRC Connection Reconfiguration message in LTE-advanced technology.The control message may modify an RRC connection. The control messagemay include an RRC transaction identifier. The control message may be anRRC connection set up message. The wireless device may transmit aresponse message after it receives the control message. The responsemessage may include a preferred PLMN ID.

The control message may configure the signal quality metric that thewireless device measures. The control message may configure measurementreporting criteria. The control message may configure cross carrierscheduling configuration. The cross carrier scheduling configuration mayassociate one non-backward compatible carrier in the at least onenon-backward compatible carrier with a backward compatible carrier inthe at least one backward compatible carrier.

According to some of the various aspects of embodiments, the controlmessage may comprise physical channel configuration, the physicalchannel configuration may comprise cross carrier schedulingconfiguration. The control message may comprise radio resourceconfiguration. The radio resource configuration may comprise physicalchannel configuration. The carrier identifier may a carrier index. Theremay be multiple alternatives for reference signal transmission. Thecommon reference signal may not transmitted on the at least onenon-backward compatible carrier. The common reference signal may betransmitted in a pre-configured subset of the subframes on the at leastone non-backward compatible carrier. The common reference signal may betransmitted in PDCCH radio resource on the at least one non-backwardcompatible carrier. The common reference signal may be transmitted onthe at least one non-backward compatible carrier. CSI reference signalmay be transmitted on the at least one non-backward compatible carrier.CSI reference signal may be transmitted on the at least one backwardcompatible carrier. Demodulation reference signal may be transmitted onthe at least one non-backward compatible carrier. Demodulation referencesignal may be transmitted on the at least one backward compatiblecarrier.

According to some of the various aspects of embodiments, the basestation may transmit a plurality of control messages to the wirelessdevice on a backward compatible carrier. The plurality of controlmessages may comprise scheduling information for transmission of packetson a non-backward compatible carrier associated with the backwardcompatible carrier. The base station may transmit a plurality of packetsto the wireless device on the non-backward compatible carrier accordingto the scheduling information. The plurality of control messages may bePDCCH control messages. One of the at least one backward compatiblecarrier may be a primary cell carrier for the wireless device. Thechannel state information may comprise at least CQI information, and/orrank indicator information, and/or precoding matrix indicatorinformation. The format of the channel state information may beconfigured by the control message.

According to some of the various aspects of embodiments, base stationsin a wireless network may be directly or indirectly connected to eachother to exchange signaling and data packets. This interface in LTE andLTE-Advanced may be called X2 interface. Other embodiment of theinterface may also possible, for example using S1 interface. The X2 userplane interface (X2-U) may be defined between base stations. The X2-Uinterface may provide non-guaranteed delivery of user plane PDUs. Thetransport network layer may be built on IP transport and GTP-U may beused on top of UDP/IP to carry the user plane PDUs. The X2 control planeinterface (X2-CP) may be defined between two neighbor base stations. Thetransport network layer may be built on SCTP on top of IP. Theapplication layer signaling protocol may be referred to as X2-AP (X2Application Protocol). A single SCTP association per X2-C interfaceinstance may be used with one pair of stream identifiers for X2-C commonprocedures. A few pairs of stream identifiers may be used for X2-Cdedicated procedures. The list of functions on interface between thebase stations may include the following: mobility support, loadmanagement, inter-cell interference coordination, and data exchange.

In order to establish an association between two base stations, a firstbase station sends a first message to a second base station to initiatean association between two endpoints. The first initiation message maycomprise the following parameters: Initiate tag, advertised receiverwindow credit, number of outbound streams, number of inbound streams,and an initial transmit sequence number.

Initiation Tag may be a 32-bits unsigned integer. The receiver of theinitiation message (the responding end) may record the value of theinitiate tag parameter. This value may be placed into the verificationtag field of every SCTP packet that the receiver of the initiationmessage transmits within this association. The initiation tag may beallowed to have any value except zero.

Advertised receiver window credit may be thirty-two bits unsignedinteger. This value may represent the dedicated buffer space, in termsof the number of bytes, the sender of the initiation message may bereserved in association with this window. During the life of theassociation, this buffer space may not be lessened (e.g., dedicatedbuffers taken away from this association); however, an endpoint maychange the value of window credit it sends in a packet. Number ofoutbound streams may be sixteen bits unsigned integer. It may define thenumber of outbound streams the sender of this initiation message wishesto create in this association. Number of inbound streams may be sixteenbits unsigned integer. It may define the maximum number of streams thesender of this initiation message may allow the peer end to create inthis association. There may be no negotiation of the actual number ofstreams but instead the two endpoints may use the minimum of requestedand offered parameters. Initial transmit sequence number may bethirty-two bits unsigned integer. Initial transmit sequence number maydefine the initial transmit sequence number that the sender may use.This field may be set to the value of the initiate tag field.

According to some of the various aspects of embodiments, the second basestation may transmit an initiation acknowledgement message toacknowledge the initiation of an SCTP association with the first basestation. The parameter part of the initiation acknowledgement messagemay be formatted similarly to the initiation message. The parameter partmay use two extra variable parameters: The state cookie and theunrecognized parameter. Initiate tag may be a thirty-two bits unsignedinteger. The receiver of the initiation acknowledgement message mayrecord the value of the initiate tag parameter. This value may be placedinto the verification tag field of every SCTP packet that the initiationacknowledgement message receiver transmits within this association.Advertised receiver window credit may be a thirty-two bits unsignedinteger. This value may represent the dedicated buffer space, in termsof the number of bytes, the sender of the initiation acknowledgementmessage has reserved in association with this window. During the life ofthe association, this buffer space may not be lessened (e.g., dedicatedbuffers taken away from this association).

According to some of the various aspects of embodiments, number ofoutbound streams may be represented by sixteen bits unsigned integer.Number of outbound streams may define the number of outbound streams thesender of this initiation acknowledgement message wishes to create inthis association. Number of inbound streams may be a represented interms of sixteen bits unsigned integer. It may define the maximum numberof streams the sender of this initiation acknowledgement message allowsthe peer end to create in this association. There may not be negotiationof the actual number of streams but instead the two endpoints may usethe minimum of requested and offered parameters. Initial transmitsequence number (TSN) may be a represented by thirty-two bits unsignedinteger. Initial transmit sequence number (TSN) may define the initialTSN that the initiation acknowledgement message sender may use. Thisfield may be set to the value of the initiate tag field. The statecookie parameter may contain the needed state and parameter informationrequired for the sender of this initiation acknowledgement message tocreate the association, along with a message authentication code (MAC).Unrecognized parameter may be returned to the originator of theinitiation message when the initiation message contains an unrecognizedparameter that has a value that indicates it should be reported to thesender. This parameter value field may contain unrecognized parameterscopied from the initiation message complete with parameter type, length,and value fields.

According to some of the various aspects of embodiments, when sending aninitiation acknowledgement message as a response to an initiationmessage, the sender of initiation acknowledgement message may create astate cookie and sends it in the state cookie parameter of theinitiation acknowledgement message. Inside this state cookie, the sendermay include a message authentication code, a timestamp on when the statecookie is created, and the lifespan of the state cookie, along with theinformation needed for it to establish the association. The followingsteps may be taken to generate the state cookie: 1) create anassociation transmission control block (TCB) using information from boththe received initiation and the outgoing initiation acknowledgementmessages, 2) In the TCB, set the creation time to the current time ofday, and the lifespan to the protocol parameter to a pre-determinednumber, 3) From the TCB, identify and collect the minimal subset ofinformation needed to re-create the TCB, and generate a MAC using thissubset of information and a secret key, and/or 4) Generate the statecookie by combining this subset of information and the resultant MAC.

After sending the initiation acknowledgement with the state cookieparameter, the sender may delete the TCB and any other local resourcerelated to the new association, so as to prevent resource attacks. Thehashing method used to generate the MAC is strictly a private matter forthe receiver of the initiation message. The use of a MAC is used toprevent denial-of-service attacks. The secret key may be random. It maybe changed reasonably frequently, and the timestamp in the state cookiemay be used to determine which key should be used to verify the MAC. Animplementation may make the cookie as small as possible to ensureinteroperability.

According to some of the various aspects of embodiments, the first basestation may transmit at least one third message to the second basestation. One of the at least one third message may be cookie-echomessage. The cookie-echo message may be used during the initializationof an association. It may be sent by the initiator of an association toits peer to complete the initialization process. This message mayprecede any transport packet message sent within the association, butmay be bundled with one or more data transport packet in the samepacket. This message may contain the exact cookie received in the statecookie parameter from the previous initiation acknowledgement message.The type and flags of the cookie-echo may be different than the cookieparameter. An implementation may make the cookie as small as possible toensure interoperability. A cookie echo may not contain a state cookieparameter, instead, the data within the state cookie's parameter valuebecomes the data within the cookie echo's chunk value. This may allow animplementation to change the first two bytes of the state cookieparameter to become a cookie echo message. The first base station maytransmit at least one application protocol message in cookie echomessage. Or the base station may choose to transmit application protocolmessages after the association is complete and do not includeapplication protocol messages in cookie-echo message. This is animplementation option.

The application protocol message may receive a cookie-ack message fromthe second base station. This message may be used during theinitialization of an association. It may be used to acknowledge thereceipt of a cookie-echo message. This message may precede any data sentwithin the association, but may be bundled with one or more data packetsin the same SCTP packet. The second base station may transmit at leastone application protocol message in cookie ack message. Or the basestation may choose to transmit application protocol messages after theassociation is complete and may not include application protocolmessages in cookie-ack message. This could be an implementation option.

After the initiation and initiation acknowledgement messages aretransmitted, the first base station or the second base station maytransmit an X2 setup message to set up an X2 application interface. Thefirst base station or the second base station may wait until theassociation is complete to set up an X2 application interface. Eitherfirst base station or second base station could start the set up of anX2 application. The purpose of the X2 setup procedure could be toexchange application level configuration data needed for two basestations to interoperate correctly over the X2 interface. This proceduremay erase any existing application level configuration data in the twonodes and replace it by the one received. This procedure may also resetthe X2 interface like a reset procedure would do.

A first base station or second base station may initiate the procedureby sending the X2 set up request message to a candidate base station.The candidate base station may reply with the X2 set up responsemessage. The initiating base station may transfer the list of servedcells. The candidate base station may reply with the complete list ofits served cells in the reply.

According to some of the various aspects of embodiments, the X2 set uprequest message may include the following information about theoriginator of the message: a global base station identifier, theinformation about the served cells, and a GU group identifier list. GUGroup identifier list is the pools to which the base station belongs to.Each row in this list may include the PLMN ID and MME group Identifier.The information about each served cell may include information about theserved cell configurations. It may also include the list of neighborcells of the served cell including: Cell global identifier of theneighbor cell, Physical cell identifier of the neighbor cell, andfrequency. The served cell information may include at least one of thefollowing parameters: Physical cell ID, global cell identifier, trackingarea code, at least one broadcast PLMN, FDD information (uplink anddownlink frequencies, uplink and downlink transmission bandwidth), TDDinformation (transmission frequency, subframe assignment, specialsubframe information, special subframe pattern, cyclic prefix fordownlink and uplink), number of antenna ports, PRACH configuration,MBSFN subframe info (radio frame allocation period, radio frameallocation offset, subframe allocation), and CSG identifier. The X2 setup request message may also include information identifying the servedcell downlink or/and uplink carrier type. This information may beincluded explicitly or implicitly in the served cell configuration. Thecarrier type here could be a first, second, or third carrier type. Forexample, carrier type may be broadly identified as backward compatiblecarrier and non-backward compatible carriers. In other exampleembodiment, the categorization may be different. Each served cellincludes a downlink carrier. The carrier types may be called usingvarious names such as data carriers, data cells, control carriers,control cells, primary cells, primary carriers, secondary cells,secondary carriers, or other example names. Each cell includes adownlink carrier and may or may not include an uplink carrier. A celltype may implicitly indicate a carrier type in some example embodiments.The backward compatible and non-backward compatible may be functionalcharacteristics of the carriers and may not be reflected in the carriertypes names. The carrier type may not be explicitly indicated in themessages, but this information may be implicitly obtained from themessages. For example, an X2 set up request, may identify cell types A,B, C, and D. Cell type A, B, and C may include backward compatiblecarrier(s), and cell type D may include non-backward compatiblecarrier(s). The information about which carrier is backward compatibleand which carrier is not backward compatible may be implicitlydetermined based on the definition of cell types A, B, C, and D. Forexample, a backward compatible carrier may be used by all wirelessdevices of release 10 and beyond. But a non-backward compatible carriermay be used by wireless devices of release 11 and beyond.

X2 set up response messages may include most or all of the fields of theX2 set up request message characterizing the base station that istransmitting the message. After two base stations exchange X2 set uprequest and response message, base stations may be aware of the otherbase station configurations including information about its servingcells. This information may be used to perform various functionsperformed by X2 interface including handover signaling and management,load management, and interference coordination.

According to some of the various aspects of embodiments, a first basestation may receive a second application protocol message from a secondbase station in the plurality of base stations. The second applicationprotocol message may comprise at least one of the following: anidentifier of the second base station, at least one MME groupidentifier, cell identifier for each of the at least one backwardcompatible carrier, and/or information identifying a carrier type foreach carrier in the plurality of carriers. The carrier type may be oneof at least a first carrier type and a second carrier type. The secondbase station may comprise a plurality of carriers comprising at leastone backward compatible carrier, and at least one non-backwardcompatible carrier. A first common reference signal overhead of each ofthe at least one non-backward compatible carrier may be substantiallylower than a second common reference signal overhead of each of the atleast one backward compatible carrier. The carrier type may be one ofbackward compatible carrier type and non-backward compatible carriertype. The first base station may operate a wireless device handoverbased, at least in part, on information in the second applicationprotocol message. The information in the second application protocol maybe used to make a handover decision and/or to prepare the wirelessdevice for handover. For example, the information in the secondapplication protocol may be used by the first base station tocommunicate with the second base station. The first base station mayalso use the information to decide whether the first base station shouldinitiate a handover to the second base station. Some other parameters,such as cell identifiers and MME identifiers may be used by the firstbase station to analyze the measurement information received from theUE.

According to some of the various aspects of embodiments, the applicationprotocol messages communicated between two neighboring base stations mayexchange application level configuration data needed for two basestations to interoperate correctly over the X2 interface. A handoverbetween two neighboring base stations may not take place, before thebase stations exchange first and second application protocol messages.Information in the first and second application protocol messages may beused by a base station for making a handover decision. For example,neighbor information, cell information, carrier information, physicalconfigurations, and/or the like may be used by a first base station tohandover a wireless device to a second base station. In an exampleembodiment, the first base station may consider information related tonon-backward compatible and backward compatible carriers to handover alegacy wireless device to a base station with a higher number ofbackward compatible carriers. In another example, the first base stationmay handover a release 11 wireless device to a base station with highernumber of non-backward compatible carriers. Various implementationspecific alternatives may be implemented to employ the information inapplication protocol messages to enhance handover mechanism.

FIG. 10 is an example flow chart showing communications between twoneighboring base stations including non-backward compatible carriers asper an aspect of an embodiment of the present invention. According tosome of the various aspects of embodiments, a first base station maytransmit a first message to initiate an association between the firstbase station and a second base station in the plurality of base stationsas shown in 1001. The first message may comprise a first initiation tag.The first base station may receive a second message from the second basestation as shown in 1003. The second message may comprise a secondverification tag, a second initiation tag, and a first state parameter.The second verification tag may be equal to the first initiation tag. Afirst state parameter may comprise at least one parameter related tooperational information of the association, and a message authenticationcode generated as a function of a private key. The first base stationmay transmit at least one third message to the second base station asshown in 1007. The at least one third message may comprise a firstverification tag, and a parameter comprising the first state parameter.The first verification tag may be equal to the second initiation tag.The first base station may receive at least one fourth message from thesecond base station as shown in 1009. The at least one fourth messagemay comprise an acknowledgement for the receipt of the parameter and asecond application protocol message. The second application protocolmessage may comprise an identifier of the second base station, at leastone MME group identifier, cell identifier for each of the at least onebackward compatible carrier, and information identifying a carrier typefor each carrier in the plurality of carriers. The second base stationmay comprise a plurality of carriers comprising at least one backwardcompatible carrier and at least one non-backward compatible carrier. Afirst common reference signal overhead of each of the at least onenon-backward compatible carrier may be lower than a second commonreference signal overhead of each of the at least one backwardcompatible carrier. The carrier type may be one of backward compatiblecarrier type and non-backward compatible carrier type. The first basestation may operate a wireless device handover using the associationand/or based, at least in part, on information in the at least onefourth message as shown in 1010.

According to some of the various aspects of embodiments, the firstinitiation tag value may be a selected in the first base station using apseudo-random process. The second initiation tag value may be selectedin the second base station using a pseudo-random process. The firstmessage may further comprise a first base station transport address anda second base station transport address. The first message may furthercomprise a first advertised receiver window credit representing adedicated buffer space that the first base station reserves for a windowof received packets from the second base station. The first message mayfurther comprise a first initial transmission sequence number that thefirst base station uses for transmission of data segments. The firstinitial transmission sequence number may be equal to the firstinitiation tag.

The second message may further comprise the first base station transportaddress and the second base station transport address. The secondmessage may further comprise a second advertised receiver window creditrepresenting a dedicated buffer space that the second base stationreserves for a window of received packets from the first base station.The second message may further comprise a second initial transmissionsequence number that the second base station uses for transmission ofdata chunks. The second initial transmission sequence number may beequal to the second initiation tag. The at least one third message mayfurther comprise the first base station transport address and the secondbase station transport address. The at least one third message mayfurther comprise a transmit sequence number, a stream identifier, astream sequence number.

The at least one fourth message may further comprise a transmit sequencenumber, a stream identifier, and a stream sequence number. The secondbase station may place the first initiation tag in the verification tagof every transport layer packet that it transmits to the first basestation within the association. The first base station may place thesecond initiation tag in the verification tag of every SCTP packet thatit transmits to the second base station within the association. Theassociation may be an SCTP association. The at least one fourth messagemay further comprise the first base station transport address and thesecond base station transport address. The second application protocolmessage may be an X2-Application Protocol Setup Request message. Thesecond application protocol message may be an X2-Application ProtocolSetup Response message. The at least one third message may furthercomprise an X2-Application Protocol Setup Request message. The at leastone third message may further comprise an X2-Application Protocol SetupResponse message.

The first state parameter may further comprise a timestamp on when thefirst state parameter is created. The first state parameter may furthercomprise the lifespan of the first state parameter. The messageauthentication code may further be a function of at least one parameterrelated to operational information of the association. The at least onethird message may further comprise a first application protocol message.The first application protocol message may comprise a identifier of thefirst base station, at least one MME group identifier, cell identifierfor each of the at least one backward compatible carrier, informationidentifying a carrier type for each carrier in the plurality ofcarriers. The first base station may comprise a plurality of carrierscomprising at least one backward compatible carrier and at least onenon-backward compatible carrier. The carrier type may be one of backwardcompatible and non-backward compatible.

The first verification tag and the second verification tag in theassociation may not change during the life time of the association. Anew verification tag value may be used each time the first base stationor the second base station tears down and then reestablishes anassociation with the same node. The operational information comprises atleast one of the following: a parameter in the first message, aparameter in the second message, a state of the association, aconfiguration parameter of the first base station, and a configurationparameter of the second base station. The first message and the secondmessage may further comprise a checksum for packet validation. The firstbase station transport address and the second base station transportaddress may comprise an IP address and a port address. The secondapplication protocol message may further comprise cell identifier foreach of the at least one non-backward compatible carrier. The secondapplication protocol message may further comprise informationidentifying for each of the at least one non-backward compatiblecarrier, a corresponding backward compatible carrier.

There may be various alternative options for transmitting referencesignal on downlink carriers. The at least one backward compatiblecarrier may broadcast a common cell reference signal and the at leastone non-backward compatible carrier may not broadcast the common cellreference signal. The common reference signal may not be transmitted onthe at least one non-backward compatible carrier. The common referencesignal may be transmitted in a pre-configured subset of the subframes onthe at least one non-backward compatible carrier. The common referencesignal may be transmitted in PDCCH radio resource on the at least onenon-backward compatible carrier. The common reference signal may betransmitted on the at least one non-backward compatible carrier. A basestation may transmit a common reference signal on a pre-configured OFDMresource region of the at least one non-backward compatible carrier.

CSI reference signal may be transmitted on the at least one non-backwardcompatible carrier. CSI reference signal may be transmitted on the atleast one backward compatible carrier. Demodulation reference signal maybe transmitted on the at least one non-backward compatible carrier.Demodulation reference signal maybe transmitted on the at least onebackward compatible carrier.

The first message may further comprise a first number of outboundstreams that the first base station intend to create and a first maximumnumber of inbound streams that the first base station allows the secondbase station to create. The second message may further comprise a secondnumber of outbound streams that the second base station intend tocreate, a second maximum number of inbound streams the second basestation allows the first base station to create. The second number ofoutbound streams is smaller than or equal to the first maximum number ofinbound streams. The first base station may further select a numberequal or lower than the minimum of the first number of outbound streamsand the second maximum number of inbound streams as the number ofoutbound streams for the first base station.

Embodiments of the present invention enable the intelligent transfer ofa wireless device between base stations that accounts for devices thathave both backward and non-backward compatible carrier configurations.An issue with respect to non-backward compatible carrier configurationsis the maintenance and updating of carrier configurations during awireless device handover from a serving base station to a target basestation. A wireless device may be configured with a first carrierconfiguration with a serving base station. A target base station maymaintain the same non-backward compatible carrier configuration, or maydirect the updating of a wireless device's non-backward compatiblecarrier configuration. There is a need for developing a signalling flow,wireless device processes, and base station processes to addresswireless device non-backward compatible carrier configurations during ahandover to reduce handover overhead and handover delay.

According to some of the various aspects of embodiments, in connectedmode, the network may control wireless device mobility. For example, thenetwork may decide when and to which base station the wireless deviceconnects. For network controlled mobility in connected mode, a primarycarrier may be changed using an RRC connection reconfiguration messagethat includes mobility control information (handover). The network maytrigger the handover procedure (e.g. based on radio conditions, load,QoS, wireless device category, and/or the like). The network mayconfigure the wireless device to perform measurement reporting. Thenetwork may also initiate a handover blindly (e.g. without havingreceived measurement reports from the wireless device). Before sendingthe handover message to the wireless device, the source base station mayprepare one or more target cells. The source base station may select atarget primary cell. The source base station may also provide the targetbase station with a list of best cells on a frequency for whichmeasurement information is available (e.g. in order of decreasing signalstrength level). The source base station may also include availablemeasurement information for the cells provided in the list. The targetbase station may decide which backward compatible carrier(s) andnon-backward compatible carrier(s) are configured for use after thehandover, which may include cells other than the ones indicated by thesource base station.

The target base station may generate a message used to configurebackward compatible carrier(s) and non-backward compatible carrier(s) ofthe wireless device for the handover, for example, the message includingcarrier configuration parameters to be used in the target base station.The source base station may transparently (e.g., may not altervalues/content) forward the handover message/information received fromthe target base station to the wireless device. After receiving thehandover message, the wireless device may attempt to access the targetprimary cell at the available random access channel resources accordingto a random access resource selection. Upon successful completion of thehandover, the wireless device may send a message used to confirm thehandover to the target base station. The wireless device may use thetarget backward compatible and non-backward compatible carrierconfiguration received from the source base station in communicatingwith the target base station.

According to some of the various aspects of embodiments, a base stationmay consider a wireless device's capability in configuring non-backwardcompatible carriers for a wireless device. A wireless device may beconfigured with a configuration that is compatible with the wirelessdevice's capability. Capability to communicate via non-backwardcompatible carriers may not be supported by wireless devices notcompatible with LTE release 11 or above. A wireless device may transmitits capability to a base station via an RRC message. The base stationmay consider wireless device capability in configuring non-backwardcompatible carriers for the wireless device.

The wireless device context within the source base station may containinformation regarding roaming/handover restrictions which may beprovided either at connection establishment or at the last tracking areaupdate process. The source base station may configure the wirelessdevice measurement procedures employing at least one RRC connectionreconfiguration message. The wireless device may be triggered to send atleast one measurement report by the rules set by, for example: systeminformation, RRC configuration, and/or the like. The source base stationmay make a handover decision based on many parameters, such as:measurement reports, radio resource configuration information, trafficand load information, a combination of the above, and/or the like. Thesource base station may initiate the handover procedure by sending ahandover request message to one or more potential target base stations.

The source base station may transmit a handover request message to oneor more potential target base stations by passing information to preparethe handover at the target side. The handover request message maycomprise information indicating the wireless device's capabilityregarding communication employing non-backward compatible carrier(s)and/or backward compatible carrier(s). The target base station mayemploy the capability of the wireless device in order to properlyconfigure carrier configuration of the wireless device before thewireless device connects to the target base station. The target basestation may configure the wireless device considering the carrierconfiguration limitations and capabilities of the wireless device. Forexample, if the wireless device does not support non-backward compatiblecarriers, or if the wireless device does not support special type(s) ofbackward compatible carriers or some carrier band combinations, thetarget base station may avoid trying to configure the wireless devicewith those carrier configuration options. In another example, if thewireless device does not support non-backward compatible carrierconfigurations with certain band combinations or synchronizationoptions, the base station may consider this limitation in wirelessdevice carrier configurations. In another example embodiment, handoverrequest messages may further comprise the current backward andnon-backward compatible carrier configuration of the wireless deviceconnected to the serving base station. During the handover preparationphase, the serving base station may transmit wireless device's carriercapability and/or wireless device's current carrier configuration(non-backward and backward carrier configuration of the wireless devicein connection with the serving base station) to one or more potentialtarget base stations. In an example embodiment, the serving base stationmay provide information such as, for example, about wireless devicededicated radio resource configurations. This may, for example, includeconfiguration of non-backward compatible carrier parameters, enhancedPDCCH parameters, PDSCH parameters, non-backward compatible physicallayer parameters and channel parameters, power control parameters,carrier configuration parameters, frequency information, carrier type,cross carrier scheduling parameters, and/or dedicated MAC configurationparameters, a combination thereof, and/or the like. This information maybe employed, at least in part, by the potential target base station toconfigure the wireless device, for example, to configure multiplecarrier configuration parameters.

Handover admission control may be performed by the target base stationdependent on many factors (e.g. QoS required for the wireless devicebearers, wireless device capabilities, wireless device configuration,target base station load, a combination of the above, and/or the like).The target base station may configure the required resources accordingto the received information from the serving base station. The radioaccess configuration to be used in the target carrier may be specifiedindependently (for example as an establishment) or as a delta comparedto the radio access configuration used in the source cell (for exampleas a reconfiguration).

The target base station may prepare a handover and may send a handoverrequest acknowledge message to a source base station. The handoverrequest acknowledge message may include a transparent container to besent to the wireless device as an RRC message to perform the handover.The container may include a new C-RNTI, target base station securityalgorithm identifiers for the selected security algorithms, a dedicatedRACH preamble, access parameters, SIB s, and/or other configurationparameters. The transparent container may further comprise the backwardcompatible and non-backward compatible carrier configurations forconnection of the wireless device to the target base station. Thecarrier configurations may modify the carrier configuration of thewireless device or may keep the same carrier configuration that thewireless device has with the serving base station. The target basestation may generate the RRC message to perform the handover, forexample, the RRC connection reconfiguration message including themobility control information. The RRC message may be sent by the sourcebase station towards the wireless device. The source base station mayperform the necessary integrity protection and ciphering of the message.The wireless device may receive the RRC connection reconfigurationmessage from the source base station and may start performing thehandover.

After receiving the RRC connection reconfiguration message, includingthe mobility control information, the wireless device may performsynchronization to the target base station and access the target cellvia a random access channel on a primary cell. The wireless device mayderive target base station specific keys and may configure the selectedsecurity algorithms to be used in the target cell. The target basestation may respond with uplink allocation and timing advanceinformation. After the wireless device has successfully accessed thetarget cell, the wireless device may send an RRC connectionreconfiguration complete message to confirm the handover and to indicatethat the handover procedure is completed for the wireless device. Thetarget base station may now begin sending and receiving data with thewireless device.

FIG. 11 is an example flow chart for handover between two neighbouringbase stations including non-backward compatible carriers as per anaspect of an embodiment of the present invention. According to some ofthe various aspects of embodiments, a serving base station may beconfigured to communicate employing at least one backward compatiblecarrier and at least one non-backward compatible carrier. The servingbase station may receive a first message from a wireless device on aprimary carrier in the at least one backward compatible carrier as shownin 1101. The first message may comprise one or more parametersimplicitly or explicitly indicating whether the wireless device supportsconfiguration of one or more non-backward compatible carriers. Forexample, the first message may include a first parameter that indicateswhether the wireless device supports non-backward compatible carrierand/or a second parameter indicating what type of non-backwardcompatible carrier is supported (e.g. synchronized, unsynchronized,inter-band, intra-band, etc). In another example, the first message mayinclude a parameter indicating the release version of the wirelessdevice, which may implicitly indicate whether the wireless devicesupports non-backward compatible carrier and/or which type of backwardand non-backward compatible carriers are supported. In another example,a parameter may indicate radio capabilities which implicitly orexplicitly indicate whether the wireless device supports non-backwardcompatible carrier and/or which type of backward and non-backwardcompatible carriers are supported. The specification provides manyembodiments of backward compatible and non-backward compatible carriers.In an example embodiment, a first common reference signal overhead ofeach of the at least one non-backward compatible carrier may besubstantially lower than a second common reference signal overhead ofeach of the at least one backward compatible carrier.

The serving base station may transmit to the wireless device, at leastone second message as shown in 1103. At least some of the parameters inthe at least one second message may depend at least in part on the firstmessage. For example, if the first message indicates certain capabilityin the wireless device, the base station may configure thosecapabilities. In another example, if the first base station indicatescertain capabilities are not supported in the wireless device, the basestation may not configure those capabilities. For example, if thewireless device does not support inter-band synchronized carriers, thebase station may not configure inter-band synchronized carriers for thewireless device.

According to some of the various aspects of embodiments, the at leastone second message may comprise at least one of: an identifier for eachcarrier in the plurality of carriers, information identifying a carriertype for each of the plurality of carriers, and information associatingeach non-backward compatible carrier in the plurality of carriers withone backward compatible carrier in the plurality of carriers, and/ormeasurement parameters, and/or a combination of the above. Theidentifier for each carrier may be a carrier index, and/or a carrierphysical cell ID, and/or the like. The plurality of carriers maycomprise: at least one of the at least one backward compatible carrier,and at least one of the at least one non-backward compatible carrier.The information identifying a carrier type for each of the plurality ofcarriers may be in the form of physical layer configurationparameter(s). For example, certain parameters in the physical layer maybe configured in a way that it identifies a carrier to be a backward ornon-backward compatible carrier. For example, if common reference signalis not transmitted on a carrier, the carrier may be a non-backwardcompatible carrier. In another example, if enhanced PDCCH is configuredfor a carrier that carrier may be considered to be a non-backwardcarrier. Carrier types may not be limited to backward and non-backwardcarrier types, and other carrier types may also be supported (e.g.synchronized, contiguous, non-synchronized, etc). In one exampleembodiment, the carrier type may be one of a backward compatible typeand non-backward compatible type. Information associating eachnon-backward compatible carrier in the plurality of carriers with onebackward compatible carrier in the plurality of carriers may be in theform of, for example, a backward carrier index in the non-backwardcarrier configuration parameters. In another example, the associationparameters may be included in the cross carrier scheduling configurationparameters. The at least one second message may be configured to causeconfiguration of a plurality of carriers in the wireless device. The atleast one second message may be configured to cause the wireless devicemeasuring signal quality of at least one carrier of at least one targetbase station in response to the measurement parameters.

According to some of the various aspects of embodiments, the servingbase station may receive at least one measurement report from thewireless device in response to the at least one second message as shownin 1107. The at least one measurement report may comprise signal qualityinformation of at least one of the at least one carrier of at least oneof the at least one target base station. The signal quality informationmay be derived at least in part employing measurements of at least oneOFDM subcarrier. The serving base station may make a handover decision,based at least in part on the at least one measurement report as shownin 1109. The serving base station may transmit, in response to theserving base station making a handover decision for the wireless device,at least one third message to at least one target base station as shownin 1110. The at least one third message may comprise at least one of:the one or more parameters indicating whether the wireless devicesupports configuration of one or more non-backward compatible carriers;and configuration information of some of the carriers. The some of thecarriers may include the at least one of the at least one backwardcompatible carrier and/or the at least one of the at least onenon-backward compatible carrier.

According to some of the various aspects of embodiments, before the atleast one second message is transmitted, the serving base station mayencrypt the at least one second message. The serving base station mayalso protect the at least one second message by an integrity header. Theat least one second message may further include configurationinformation for physical channels for the wireless device. The at leastone second message may be configured to cause the wireless device to setup or modify at least one radio bearer. One of the at least one secondmessage may be configured to cause the wireless device to configure atleast one of a physical layer parameter, a MAC layer parameter and/or anRLC layer parameter. One of the at least one second message comprisesradio link configuration information comprising uplink channelconfiguration parameters and handover parameters. At least one of the atleast one second message may comprise a radio resource configurationcomprising a physical channel configuration. The serving base stationmay transmit a channel state information reference signal on the atleast one non-backward compatible carrier and/or the at least onebackward compatible carrier. The serving base station may transmit ademodulation reference signal on the at least one non-backwardcompatible carrier and the at least one backward compatible carrier. Aformat of the at least one measurement report may be determinedemploying at least one of the at least one second control message.

FIG. 12 is an example flow chart for handover between two neighbouringbase stations including non-backward compatible carriers as per anaspect of an embodiment of the present invention. According to some ofthe various aspects of embodiments, a cellular network may comprise aserving base station and a target base station. The serving base stationmay transmit, in response to the serving base station making a handoverdecision for a wireless device, at least one first message to at leastone target base station as shown in 1201. The serving base station mayreceive, at least one second message from one of the at least one targetbase station as shown in 1203. The at least one second message maycomprise at least one of: configuration parameters of a plurality ofcarriers for the wireless device, information identifying a carrier typefor each of the plurality of carriers, information associating each ofthe at least one non-backward compatible carrier with one of the atleast one backward compatible carrier.

According to some of the various aspects of embodiments, the pluralityof carriers may comprise at least one backward compatible carrier and atleast one non-backward compatible carrier. Many example embodiments ofbackward compatible carrier and non-backward compatible carriers aredisclosed in the specification. In an example embodiment, a first commonreference signal overhead of each of the at least one non-backwardcompatible carrier may be substantially lower than a second commonreference signal overhead of each of the at least one backwardcompatible carrier. The carrier type may be one of a backward compatibletype and non-backward compatible type. The serving base station maytransmit, in response to receiving the at least one second message, athird message to the wireless device as shown in 1207. The third messagemay comprise the configuration information of the at least one backwardcompatible carrier and/or the at least one non-backward compatiblecarrier.

Before the third message is transmitted, the serving base station mayencrypt the third message. The serving base station may protect thethird message by an integrity header.

The third message may further include configuration information forphysical channels for the wireless device. The third message may beconfigured to cause the wireless device to set up or modify at least oneradio bearer. The third message may be configured to cause the wirelessdevice to configure at least one of a physical layer parameter, a MAClayer parameter and/or an RLC layer parameter.

The third message may comprise radio link configuration informationcomprising uplink channel configuration parameters and/or handoverparameters. The third message may comprise at least one radio resourceconfiguration parameter comprising at least one physical channelconfiguration parameter. The one of the at least one target base stationmay transmit a channel state information reference signal on the atleast one non-backward compatible carrier and the at least one backwardcompatible carrier. The one of the at least one target base station maytransmit a demodulation reference signal on the at least onenon-backward compatible carrier and the at least one backward compatiblecarrier. The third message may further comprise the informationidentifying a carrier type for each of the plurality of carriers. Thethird message may further comprise the information associating eachnon-backward compatible carrier in the plurality of carriers with onebackward compatible carrier in the plurality of carriers.

In this specification, “a” and “an” and similar phrases are to beinterpreted as “at least one” and “one or more.” In this specification,the term “may” is to be interpreted as “may, for example,” In otherwords, the term “may” is indicative that the phrase following the term“may” is an example of one of a multitude of suitable possibilities thatmay, or may not, be employed to one or more of the various embodiments.If A and B are sets and every element of A is also an element of B, A iscalled a subset of B. In this specification, only non-empty sets andsubsets are considered. For example, possible subsets of B={cell1,cell2} are: {cell1}, {cell2}, and {cell1, cell2}.

The mechanisms described in this disclosure may be implemented inhardware, software in combination with hardware, firmware, wetware (i.ehardware with a biological element) or a combination thereof, all ofwhich are behaviorally equivalent. For example, mechanisms may beimplemented as a software routine written in a computer languageconfigured to be executed by a hardware machine (such as C, C++,Fortran, Java, Basic, Matlab or the like) or a modeling/simulationprogram such as Simulink, Stateflow, GNU Octave, or Lab VIEWMathScript.Additionally, it may be possible to implement modules using physicalhardware that incorporates discrete or programmable analog, digitaland/or quantum hardware. Examples of programmable hardware comprise:computers, microcontrollers, microprocessors, application-specificintegrated circuits (ASICs); field programmable gate arrays (FPGAs); andcomplex programmable logic devices (CPLDs). Computers, microcontrollersand microprocessors are programmed using languages such as assembly, C,C++ or the like. FPGAs, ASICs and CPLDs are often programmed usinghardware description languages (HDL) such as VHSIC hardware descriptionlanguage (VHDL) or Verilog that configure connections between internalhardware modules with lesser functionality on a programmable device.Finally, it needs to be emphasized that the above mentioned technologiesare often used in combination to achieve the result of a functionalmodule.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevantart(s) that various changes in form and detail can be made thereinwithout departing from the spirit and scope. In fact, after reading theabove description, it will be apparent to one skilled in the relevantart(s) how to implement alternative embodiments. Thus, the presentembodiments should not be limited by any of the above describedexemplary embodiments. In particular, it should be noted that, forexample purposes, the above explanation has focused on the example(s)using FDD communication systems. However, one skilled in the art willrecognize that embodiments of the invention may also be implemented inTDD communication systems. The disclosed methods and systems may beimplemented in wireless or wireline systems. The features of variousembodiments presented in this invention may be combined. One or manyfeatures (method or system) of one embodiment may be implemented inother embodiments. Only a limited number of example combinations areshown to indicate to one skilled in the art the possibility of featuresthat may be combined in various embodiments to create enhancedtransmission and reception systems and methods.

The invention claimed is:
 1. A method comprising: transmitting, by afirst base station, to a second base station, and based on a handoverdecision for a wireless device, information indicating a carrier typefor each of a plurality of carriers associated with the wireless device,wherein the plurality of carriers comprises: at least one carrier of afirst carrier type that comprises a reference signal in every downlinksubframe of a plurality of downlink subframes; and at least one carrierof a second carrier type that is without a reference signal in at leastone downlink subframe of the plurality of downlink subframes; andcausing, by the first base station, handover of the wireless device fromthe first base station to the second base station.
 2. The method ofclaim 1, wherein the at least one carrier of the second carrier type iswithout the reference signal, in the at least one downlink subframe,based on data being transmitted in fewer than all downlink subframes ofthe plurality of downlink subframes.
 3. The method of claim 1, whereinthe at least one carrier of the second carrier type selectivelycomprises the reference signal based on data being transmitted in one ormore of the plurality of downlink subframes.
 4. The method of claim 1,wherein the at least one carrier of the second carrier type supportsfewer transmission modes than the at least one carrier of the firstcarrier type.
 5. The method of claim 1, wherein the at least one carrierof the second carrier type employs a wireless-device-specificdemodulation reference signal.
 6. The method of claim 1, furthercomprising causing a downlink subframe of the at least one carrier ofthe second carrier type to become empty.
 7. The method of claim 1,wherein the at least one carrier of the second carrier type comprises asecond downlink subframe in which a control channel is configured tostart at a symbol after a first symbol in the second downlink subframe.8. The method of claim 7, wherein in the second downlink subframe, noreference signal is transmitted between the first symbol in the seconddownlink subframe and the control channel in the second downlinksubframe.
 9. The method of claim 1, wherein the first base station ispart of a long-term evolution (LTE) network.
 10. A method comprising:transmitting, by a first base station, to a second base station, andbased on a handover decision for a wireless device, informationindicating a carrier type for each of a plurality of carriers associatedwith the wireless device, wherein the plurality of carriers comprises:at least one carrier of a first carrier type that comprises a referencesignal in every downlink subframe of a plurality of downlink subframes;and at least one carrier of a second carrier type that comprises areference signal in fewer than all downlink subframes of the pluralityof downlink subframes; and causing, by the first base station, handoverof the wireless device from the first base station to the second basestation.
 11. The method of claim 10, wherein the at least one carrier ofthe second carrier type is without the reference signal, in at least onedownlink subframe of the plurality of downlink subframes, based on databeing transmitted in fewer than all downlink subframes of the pluralityof downlink subframes.
 12. The method of claim 10, wherein the at leastone carrier of the second carrier type selectively comprises thereference signal based on data being transmitted in one or more of theplurality of downlink subframes.
 13. The method of claim 10, wherein theat least one carrier of the second carrier type supports fewertransmission modes than the at least one carrier of the first carriertype.
 14. The method of claim 10, wherein the at least one carrier ofthe second carrier type employs a wireless-device-specific demodulationreference signal.
 15. The method of claim 10, further comprising causinga downlink subframe of the at least one carrier of the second carriertype to become empty.
 16. The method of claim 10, wherein the at leastone carrier of the second carrier type comprises a second downlinksubframe in which a control channel is configured to start at a symbolafter a first symbol in the second downlink subframe.
 17. The method ofclaim 16, wherein in the second downlink subframe, no reference signalis transmitted between the first symbol in the second downlink subframeand the control channel in the second downlink subframe.
 18. The methodof claim 10, wherein the first base station is part of a long-termevolution (LTE) network.
 19. A method comprising: transmitting, by afirst base station, to a second base station, and based on a handoverdecision for a wireless device, information indicating a carrier typefor each of a plurality of carriers associated with the wireless device,wherein the plurality of carriers comprises: at least one carrier of afirst carrier type that comprises a reference signal in every downlinksubframe of a plurality of downlink subframes; and at least one carrierof a second carrier type that selectively comprises a reference signalin at least one downlink subframe of the plurality of downlink subframesbased on data being transmitted in one or more of the plurality ofdownlink subframes; and causing, by the first base station, handover ofthe wireless device from the first base station to the second basestation.
 20. The method of claim 19, wherein the at least one carrier ofthe second carrier type is without the reference signal in at least onesecond downlink subframe of the plurality of downlink subframes.
 21. Themethod of claim 19, wherein the at least one carrier of the secondcarrier type is without the reference signal, in at least one seconddownlink subframe of the plurality of downlink subframes, based on databeing transmitted in fewer than all downlink subframes of the pluralityof downlink subframes.
 22. The method of claim 19, wherein the at leastone carrier of the second carrier type supports fewer transmission modesthan the at least one carrier of the first carrier type.
 23. The methodof claim 19, wherein the at least one carrier of the second carrier typeemploys a wireless-device-specific demodulation reference signal. 24.The method of claim 19, further comprising causing a downlink subframeof the at least one carrier of the second carrier type to become empty.25. The method of claim 19, wherein the at least one carrier of thesecond carrier type comprises a second downlink subframe in which acontrol channel is configured to start at a symbol after a first symbolin the second downlink subframe.
 26. The method of claim 25, wherein inthe second downlink subframe, no reference signal is transmitted betweenthe first symbol in the second downlink subframe and the control channelin the second downlink subframe.
 27. The method of claim 19, wherein thefirst base station is part of a long-term evolution (LTE) network.
 28. Anon-transitory computer-readable medium storing instructions that, whenexecuted, configure a first base station to: transmit, to a second basestation and based on a handover decision for a wireless device,information indicating a carrier type for each of a plurality ofcarriers associated with the wireless device, wherein the plurality ofcarriers comprises: at least one carrier of a first carrier type thatcomprises a reference signal in every downlink subframe of a pluralityof downlink subframes; and at least one carrier of a second carrier typethat is without a reference signal in at least one downlink subframe ofthe plurality of downlink subframes; and cause handover of the wirelessdevice from the first base station to the second base station.
 29. Thenon-transitory computer-readable medium of claim 28, wherein the atleast one carrier of the second carrier type is without the referencesignal, in the at least one downlink subframe, based on data beingtransmitted in fewer than all downlink subframes of the plurality ofdownlink subframes.
 30. The non-transitory computer-readable medium ofclaim 28, wherein the at least one carrier of the second carrier typeselectively comprises the reference signal based on data beingtransmitted in one or more of the plurality of downlink subframes. 31.The non-transitory computer-readable medium of claim 28, wherein theinstructions, when executed, further cause a downlink subframe of the atleast one carrier of the second carrier type to become empty.
 32. Thenon-transitory computer-readable medium of claim 28, wherein the atleast one carrier of the second carrier type comprises a second downlinksubframe in which a control channel is configured to start at a symbolafter a first symbol in the second downlink subframe.
 33. Thenon-transitory computer-readable medium of claim 32, wherein in thesecond downlink subframe, no reference signal is transmitted between thefirst symbol in the second downlink subframe and the control channel inthe second downlink subframe.
 34. A non-transitory computer-readablemedium storing instructions that, when executed, configure a first basestation to: transmit, to a second base station and based on a handoverdecision for a wireless device, information indicating a carrier typefor each of a plurality of carriers associated with the wireless device,wherein the plurality of carriers comprises: at least one carrier of afirst carrier type that comprises a reference signal in every downlinksubframe of a plurality of downlink subframes; and at least one carrierof a second carrier type that comprises a reference signal in fewer thanall downlink subframes of the plurality of downlink subframes; and causehandover of the wireless device from the first base station to thesecond base station.
 35. The non-transitory computer-readable medium ofclaim 34, wherein the at least one carrier of the second carrier type iswithout the reference signal, in at least one downlink subframe of theplurality of downlink subframes, based on data being transmitted infewer than all downlink subframes of the plurality of downlinksubframes.
 36. The non-transitory computer-readable medium of claim 34,wherein the at least one carrier of the second carrier type selectivelycomprises the reference signal based on data being transmitted in one ormore of the plurality of downlink subframes.
 37. The non-transitorycomputer-readable medium of claim 34, wherein the instructions, whenexecuted, further cause a downlink subframe of the at least one carrierof the second carrier type to become empty.
 38. The non-transitorycomputer-readable medium of claim 34, wherein the at least one carrierof the second carrier type comprises a second downlink subframe in whicha control channel is configured to start at a symbol after a firstsymbol in the second downlink subframe.
 39. The non-transitorycomputer-readable medium of claim 38, wherein in the second downlinksubframe, no reference signal is transmitted between the first symbol inthe second downlink subframe and the control channel in the seconddownlink subframe.
 40. A non-transitory computer-readable medium storinginstructions that, when executed, configure a first base station to:transmit, to a second base station and based on a handover decision fora wireless device, information indicating a carrier type for each of aplurality of carriers associated with the wireless device, wherein theplurality of carriers comprises: at least one carrier of a first carriertype that comprises a reference signal in every downlink subframe of aplurality of downlink subframes; and at least one carrier of a secondcarrier type that selectively comprises a reference signal in at leastone downlink subframe of the plurality of downlink subframes based ondata being transmitted in one or more of the plurality of downlinksubframes; and cause handover of the wireless device from the first basestation to the second base station.
 41. The non-transitorycomputer-readable medium of claim 40, wherein the at least one carrierof the second carrier type is without the reference signal in at leastone second downlink subframe of the plurality of downlink subframes. 42.The non-transitory computer-readable medium of claim 40, wherein the atleast one carrier of the second carrier type is without the referencesignal, in at least one second downlink subframe of the plurality ofdownlink subframes, based on data being transmitted in fewer than alldownlink subframes of the plurality of downlink subframes.
 43. Thenon-transitory computer-readable medium of claim 40, wherein theinstructions, when executed, further cause a downlink subframe of the atleast one carrier of the second carrier type to become empty.
 44. Thenon-transitory computer-readable medium of claim 40, wherein the atleast one carrier of the second carrier type comprises a second downlinksubframe in which a control channel is configured to start at a symbolafter a first symbol in the second downlink subframe.
 45. Thenon-transitory computer-readable medium of claim 44, wherein in thesecond downlink subframe, no reference signal is transmitted between thefirst symbol in the second downlink subframe and the control channel inthe second downlink subframe.
 46. A first base station comprising: oneor more processors; and memory storing instructions that, when executedby the one or more processors, configure the first base station to:transmit, to a second base station and based on a handover decision fora wireless device, information indicating a carrier type for each of aplurality of carriers associated with the wireless device, wherein theplurality of carriers comprises: at least one carrier of a first carriertype that comprises a reference signal in every downlink subframe of aplurality of downlink subframes; and at least one carrier of a secondcarrier type that is without a reference signal in at least one downlinksubframe of the plurality of downlink subframes; and cause handover ofthe wireless device from the first base station to the second basestation.
 47. The first base station of claim 46, wherein the at leastone carrier of the second carrier type is without the reference signal,in the at least one downlink subframe, based on data being transmittedin fewer than all downlink subframes of the plurality of downlinksubframes.
 48. The first base station of claim 46, wherein the at leastone carrier of the second carrier type selectively comprises thereference signal based on data being transmitted in one or more of theplurality of downlink subframes.
 49. The first base station of claim 46,wherein the instructions, when executed by the one or more processors,further cause a downlink subframe of the at least one carrier of thesecond carrier type to become empty.
 50. A first base stationcomprising: one or more processors; and memory storing instructionsthat, when executed by the one or more processors, configure the firstbase station to: transmit, to a second base station and based on ahandover decision for a wireless device, information indicating acarrier type for each of a plurality of carriers associated with thewireless device, wherein the plurality of carriers comprises: at leastone carrier of a first carrier type that comprises a reference signal inevery downlink subframe of a plurality of downlink subframes; and atleast one carrier of a second carrier type that selectively comprises areference signal in at least one downlink subframe of the plurality ofdownlink subframes based on data being transmitted in one or more of theplurality of downlink subframes; and cause handover of the wirelessdevice from the first base station to the second base station.
 51. Thefirst base station of claim 50, wherein the at least one carrier of thesecond carrier type is without the reference signal in at least onesecond downlink subframe of the plurality of downlink subframes.
 52. Thefirst base station of claim 50, wherein the at least one carrier of thesecond carrier type is without the reference signal, in at least onesecond downlink subframe of the plurality of downlink subframes, basedon data being transmitted in fewer than all downlink subframes of theplurality of downlink subframes.
 53. The first base station of claim 50,wherein the instructions, when executed by the one or more processors,further cause a downlink subframe of the at least one carrier of thesecond carrier type to become empty.
 54. A system comprising: a firstbase station; and a second base station, wherein the first base stationis configured to: transmit, to the second base station and based on ahandover decision for a wireless device, information indicating acarrier type for each of a plurality of carriers associated with thewireless device, wherein the plurality of carriers comprises: at leastone carrier of a first carrier type that comprises a reference signal inevery downlink subframe of a plurality of downlink subframes; and atleast one carrier of a second carrier type that is without a referencesignal in at least one downlink subframe of the plurality of downlinksubframes; and cause handover of the wireless device from the first basestation to the second base station, and wherein the second base stationis configured to communicate with the wireless device after thehandover.
 55. The system of claim 54, wherein the at least one carrierof the second carrier type is without the reference signal, in the atleast one downlink subframe, based on data being transmitted in fewerthan all downlink subframes of the plurality of downlink subframes. 56.The system of claim 54, wherein the at least one carrier of the secondcarrier type selectively comprises the reference signal based on databeing transmitted in one or more of the plurality of downlink subframes.57. The system of claim 54, wherein the first base station is furtherconfigured to cause a downlink subframe of the at least one carrier ofthe second carrier type to become empty.
 58. A system comprising: afirst base station; and a second base station, wherein the first basestation is configured to: transmit, to the second base station and basedon a handover decision for a wireless device, information indicating acarrier type for each of a plurality of carriers associated with thewireless device, wherein the plurality of carriers comprises: at leastone carrier of a first carrier type that comprises a reference signal inevery downlink subframe of a plurality of downlink subframes; and atleast one carrier of a second carrier type that selectively comprises areference signal in at least one downlink subframe of the plurality ofdownlink subframes based on data being transmitted in one or more of theplurality of downlink subframes; and cause handover of the wirelessdevice from the first base station to the second base station, andwherein the second base station is configured to communicate with thewireless device after the handover.
 59. The system of claim 58, whereinthe at least one carrier of the second carrier type is without thereference signal in at least one second downlink subframe of theplurality of downlink subframes.
 60. The system of claim 58, wherein theat least one carrier of the second carrier type is without the referencesignal, in at least one second downlink subframe of the plurality ofdownlink subframes, based on data being transmitted in fewer than alldownlink subframes of the plurality of downlink subframes.
 61. Thesystem of claim 58, wherein the first base station is further configuredto cause a downlink subframe of the at least one carrier of the secondcarrier type to become empty.